{"history":[],"article":{"id":"9b18ec56-d3d7-463c-b96a-3dc0ada18277","title":"Metamaterial antenna","slug":"metamaterial-antenna","content":":::summary\n:::\n\n# \n**Metamaterial [antennas](https://bliptext.com/articles/antenna-radio)** are a class of [antennas](https://bliptext.com/articles/antenna-radio) which use [metamaterials](https://bliptext.com/articles/metamaterials) to increase performance of miniaturized ([electrically small](https://bliptext.com/articles/electrically-small-antenna)) [antenna systems](https://bliptext.com/articles/antenna-radio).\nTheir purpose, as with any electromagnetic antenna, is to launch [energy](https://bliptext.com/articles/energy) into free space.\nHowever, this class of antenna incorporates metamaterials, which are materials engineered with novel, often [microscopic](https://bliptext.com/articles/microscopic), structures to produce unusual [physical properties](https://bliptext.com/articles/physical-properties).\nAntenna designs incorporating metamaterials can step-up the antenna's radiated [power](https://bliptext.com/articles/power-physics).\nConventional antennas that are very small compared to the [wavelength](https://bliptext.com/articles/wavelength) reflect most of the signal back to the source.\nA metamaterial antenna behaves as if it were much larger than its actual size, because its novel structure stores and re-radiates energy.\nEstablished lithography techniques can be used to print metamaterial elements on a [printed circuit board](https://bliptext.com/articles/printed-circuit-board).\nThese novel antennas aid applications such as portable interaction with satellites, wide angle beam steering, emergency communications devices, [micro-sensors](https://bliptext.com/articles/sensor) and portable [ground-penetrating radars](https://bliptext.com/articles/radar) to search for geophysical features.\nSome applications for metamaterial antennas are [wireless communication](https://bliptext.com/articles/wireless-communication), [space communications](https://bliptext.com/articles/space-communications-and-navigation-program), [GPS](https://bliptext.com/articles/gps), [satellites](https://bliptext.com/articles/satellite), space vehicle navigation and airplanes.\n# [This Z antenna tested at the National Institute of Standards and Technology is smaller than a standard antenna with comparable properties. Its high efficiency is derived from the \"Z element\" inside the square that acts as a metamaterial, greatly boosting the radiated signal. The square is 30 millimeters on a side. | upload.wikimedia.org/wikipedia/commons/6/63/Z///Antennas///at///UHF///Frequencies.jpg]\n\n# Antennas designs\nAntenna designs incorporating metamaterials can step-up the radiated [power](https://bliptext.com/articles/power-physics) of an antenna.\nThe newest metamaterial antennas radiate as much as 95 percent of an input [radio signal](https://bliptext.com/articles/radio-signal).\nStandard antennas need to be at least half the size of the signal wavelength to operate efficiently.\nAt [300 MHz](https://bliptext.com/articles/megahertz), for instance, an antenna would need to be half a meter long.\nIn contrast, experimental metamaterial antennas are as small as one-fiftieth of a wavelength, and could have further decreases in size.\nMetamaterials are a basis for further miniaturization of [microwave antennas](https://bliptext.com/articles/microwave-antenna), with efficient power and acceptable bandwidth.\nAntennas employing metamaterials offer the possibility of overcoming restrictive efficiency-bandwidth limitations for conventionally constructed, miniature antennas.\nMetamaterials permit smaller antenna elements that cover a wider [frequency range](https://bliptext.com/articles/frequency-range), thus making better use of available space for space-constrained cases.\nIn these instances, miniature antennas with high gain are significantly relevant because the radiating elements are combined into large antenna arrays.\nFurthermore, metamaterials' negative [refractive index](https://bliptext.com/articles/refractive-index) focuses [electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation) by a [flat lens](https://bliptext.com/articles/flat-lens) versus being dispersed.\n\n## The DNG shell\nThe earliest research in metamaterial antennas was an analytical study of a miniature dipole antenna surrounded with a metamaterial.\nThis material is known variously as a negative index metamaterial (NIM) or double negative metamaterial (DNG) among other names.\nThis configuration analytically and numerically appears to produce an order of magnitude increase in power.\nAt the same time, the reactance appears to offer a corresponding decrease.\nFurthermore, the DNG shell becomes a natural impedance matching network for this system.\n\n# Ground plane applications\nMetamaterials employed in the [ground planes](https://bliptext.com/articles/ground-plane) surrounding antennas offer improved isolation between [radio frequency](https://bliptext.com/articles/radio-frequency), or [microwave](https://bliptext.com/articles/microwave) channels of ([multiple-input multiple-output](https://bliptext.com/articles/multiple-input-multiple-output)) (MIMO) [antenna arrays](https://bliptext.com/articles/phased-array).\nMetamaterial, [high-impedance groundplanes](https://bliptext.com/articles/tunable-metamaterials) can also improve [radiation](https://bliptext.com/articles/radio-frequency) efficiency and axial ratio performance of low-profile antennas located close to the [ground plane surface](https://bliptext.com/articles/ground-plane).\nMetamaterials have also been used to increase [beam scanning](https://bliptext.com/articles/microwave-scanning-beam-landing-system) range by using both the forward and backward waves in leaky wave antennas.\nVarious metamaterial antenna systems can be employed to support surveillance sensors, communication links, navigation systems and command and control systems.\n\n# Novel configurations\nBesides antenna miniaturization, the novel configurations have potential applications ranging from radio frequency devices to optical devices.\nOther combinations, for other devices in metamaterial antenna subsystems are being researched.\nEither [double negative metamaterial](https://bliptext.com/articles/double-negative-metamaterial) slabs are used exclusively or combinations of [double positive (DPS)](https://bliptext.com/articles/metamaterial) with DNG slabs, or [epsilon-negative (ENG)](https://bliptext.com/articles/metamaterial) slabs with [mu-negative (MNG)](https://bliptext.com/articles/metamaterial) slabs are employed in the subsystems.\nAntenna subsystems that are currently being researched include [cavity resonators](https://bliptext.com/articles/resonator), waveguides, scatters and antennas (radiators).\nMetamaterial antennas were commercially available by 2009.\n\n# History\n[Pendry](https://bliptext.com/articles/pendry) et al. were able to show that a three-[dimensional](https://bliptext.com/articles/dimension) array of intersecting, thin wires could be used to create negative values of [permittivity](https://bliptext.com/articles/permittivity) (\"**ε**\"), and that a periodic array of copper split ring resonators could produce an effective negative [magnetic permeability](https://bliptext.com/articles/magnetic-permeability) ( \"**μ**\").\nIn May 2000, a group of researchers, Smith et al. were the first to successfully combine the [split-ring resonator](https://bliptext.com/articles/split-ring-resonator) (SRR), with thin wire conducting posts and produce a [left-handed material](https://bliptext.com/articles/left-handed-material) that had negative values of ε, μ and [refractive index](https://bliptext.com/articles/refractive-index) for frequencies in the [gigahertz](https://bliptext.com/articles/gigahertz) or [microwave](https://bliptext.com/articles/microwave) range.\nIn 2002, a different class of negative refractive index (NRI) metamaterials was introduced that employs periodic [reactive loading](https://bliptext.com/articles/electrical-reactance) of a 2-D [transmission line](https://bliptext.com/articles/transmission-line) as the host [medium](https://bliptext.com/articles/transmission-medium).\nThis configuration used [positive index](https://bliptext.com/articles/index-of-refraction) (DPS) material with negative index material (DNG).\nIt employed a small, planar, [negative-refractive-lens](https://bliptext.com/articles/superlens) interfaced with a positive index, parallel-plate waveguide.\nThis was experimentally verified soon after.\nAlthough some SRR inefficiencies were identified, they continued to be employed as of 2009 for research.\nSRRs have been involved in wide-ranging metamaterial research, including research on metamaterial antennas.\nA more recent view is that by using SRRs as building blocks, the electromagnetic response and associated flexibility is practical and desirable.\n\n## Phase compensation due to negative refraction\nDNG can provide [phase compensation](https://bliptext.com/articles/phase-waves) due to their negative index of refraction.\nThis is accomplished by combining a slab of conventional lossless DPS material with a slab of lossless DNG metamaterial.\nDPS has a conventional positive [index of refraction](https://bliptext.com/articles/index-of-refraction), while the DNG has a negative refractive index.\nBoth slabs are [impedance](https://bliptext.com/articles/impedance-of-free-space)-matched to the outside region (e.g., free space).\nThe desired monochromatic [plane wave](https://bliptext.com/articles/plane-wave) is radiated on this configuration.\nAs this wave propagates through the first slab of material a [phase difference](https://bliptext.com/articles/phase-waves) emerges between the exit and entrance faces.\nAs the wave [propagates](https://bliptext.com/articles/wave-propagation) through the second slab the phase difference is significantly decreased and even compensated for.\nTherefore, as the wave exits the second slab the total phase difference is equal to zero.\nWith this system a phase-compensated, [waveguiding](https://bliptext.com/articles/waveguiding) system could be produced.\nBy stacking slabs of this configuration, the phase compensation (beam translation effects) would occur throughout the entire system.\nFurthermore, by changing the index of any of the DPS-DNG pairs, the speed at which the beam enters the front face, and exits the back face of the entire stack-system changes.\nIn this manner, a volumetric, low loss, time delay [transmission line](https://bliptext.com/articles/transmission-line) could be realized for a given system.\nFurthermore, this phase compensation can lead to a set of applications, which are miniaturized, [subwavelength](https://bliptext.com/articles/subwavelength), [cavity resonators](https://bliptext.com/articles/cavity-resonator), and waveguides with applications below [diffraction limits](https://bliptext.com/articles/diffraction-limit).\n\n## Transmission line dispersion compensation\nBecause of DNG's [dispersive nature](https://bliptext.com/articles/dispersion-relation) as a transmission medium, it could be useful as a dispersion compensation device for [time-domain applications](https://bliptext.com/articles/fourier-transform).\nThe dispersion produces a variance of the [group speed](https://bliptext.com/articles/group-speed) of the signals' wave components, as they propagate in the DNG medium.\nHence, stacked DNG metamaterials could be useful for modifying signal propagation along a [microstrip transmission line](https://bliptext.com/articles/microstrip).\nAt the same time, dispersion leads to distortion.\nHowever, if the dispersion could be compensated for along the microstrip line, [RF](https://bliptext.com/articles/radio-frequency) or microwave signals propagating along them would significantly decrease distortion.\nTherefore, components for attenuating distortion become less critical, and could lead to simplification of many systems.\nMetamaterials can eliminate dispersion along the microstrip by correcting for the frequency dependence of the effective permittivity.\nThe strategy is to design a length of [metamaterial](https://bliptext.com/articles/metamaterial)-loaded transmission line that can be introduced with the original length of [microstrip](https://bliptext.com/articles/microstrip) line to make the paired system [dispersionless](https://bliptext.com/articles/dispersion-optics) creating a dispersion-compensating segment of transmission line.\nThis could be accomplished by introducing a metamaterial with a specific localized [permittivity](https://bliptext.com/articles/permittivity) and a specific localized [magnetic permeability](https://bliptext.com/articles/magnetic-permeability), which then affects the relative [permittivity](https://bliptext.com/articles/permittivity) and permeability of the overall microstrip line.\nIt is introduced so that the wave impedance in the metamaterial remains unchanged.\nThe index of refraction in the medium compensates for the dispersion effects associated with the microstrip geometry itself; making the effective refractive index of the pair that of free space.\nPart of the design strategy is that the effective permittivity and permeability of such a metamaterial should be negative – requiring a DNG material.\n\n## Innovation\nCombining left-handed segments with a conventional (right-handed) transmission line results in advantages over conventional designs.\nLeft-handed transmission lines are essentially a high-pass filter with phase advance.\nConversely, right-handed transmission lines are a low-pass filter with phase lag.\nThis configuration is designated composite right/left-handed (CRLH) metamaterial.\nThe conventional Leaky Wave antenna has had limited commercial success because it lacks complete backfire-to-endfire frequency scanning capability.\nThe CRLH allowed complete backfire-to-endfire frequency scanning, including broadside.\n\n# Microwave lens\nThe [metamaterial lens](https://bliptext.com/articles/metamaterial-lens), found in metamaterial antenna systems, is used as an efficient coupler to external radiation, focusing radiation along or from a [microstrip](https://bliptext.com/articles/microstrip) transmission line into transmitting and receiving components.\nHence, it can be used as an [input device](https://bliptext.com/articles/input-device).\nIn addition, it can enhance the amplitude of [evanescent waves](https://bliptext.com/articles/evanescent-waves), as well as correct the phase of propagating waves.\n\n## Directing radiation\nIn this instance an SRR uses layers of a [metallic](https://bliptext.com/articles/metal) mesh of thin [wires](https://bliptext.com/articles/wire) – with [wires](https://bliptext.com/articles/wire) in the [three directions of space](https://bliptext.com/articles/coordinate-plane) and slices of [foam](https://bliptext.com/articles/foam).\nThis material's permittivity above the [plasma frequency](https://bliptext.com/articles/plasma-frequency) can be positive and less than one.\nThis means that the [refractive index](https://bliptext.com/articles/refractive-index) is just above zero.\nThe relevant parameter is often the contrast between the permittivities rather than the overall permittivity value at desired frequencies.\nThis occurs because the equivalent (effective) permittivity has a behavior governed by a [plasma frequency](https://bliptext.com/articles/plasma-frequency) in the microwave domain.\nThis low optical index material then is a good candidate for extremely convergent [microlenses](https://bliptext.com/articles/microlens).\nMethods that have been developed theoretically using dielectric photonic crystals applied in the microwave domain to realize a directive emitter using metallic grids.\nIn this instance, [arrayed wires in a cubic](https://bliptext.com/articles/crystal-lattice), [crystal lattice](https://bliptext.com/articles/crystal-lattice) structure can be analyzed as an array of aerials ([antenna array](https://bliptext.com/articles/phased-array)).\nAs a lattice structure it has a [lattice constant](https://bliptext.com/articles/lattice-constant).\nThe lattice constant or lattice parameter refers to the constant distance between unit cells in a crystal lattice.\nThe earlier discovery of [plasmons](https://bliptext.com/articles/plasmon) created the view that metal at [plasmon frequency](https://bliptext.com/articles/plasmon-frequency) fp is a composite material.\nThe effect of plasmons on any metal sample is to create properties in the metal such that it can behave as a [dielectric](https://bliptext.com/articles/dielectric), independent of the wave vector of the EM excitation (radiation) field.\nFurthermore, a minute-fractionally small amount of plasmon energy is absorbed into the system denoted as γ.\nFor aluminium fp = 15 eV, and γ = 0.1 eV.\nPerhaps the most important result of the interaction of metal and the plasma frequency is that permittivity is negative below the plasma frequency, all the way to the minute value of γ.\nThese facts ultimately result in the arrayed wire structure as being effectively a homogeneous medium.\nThis metamaterial allows for control of the [direction](https://bliptext.com/articles/polarization-waves) of [emission](https://bliptext.com/articles/emission-electromagnetic-radiation) of an electromagnetic radiation source located inside the material in order to collect all the [energy](https://bliptext.com/articles/energy) in a small angular domain around the [normal](https://bliptext.com/articles/surface-normal).\nBy using a slab of a metamaterial, diverging [electromagnetic waves](https://bliptext.com/articles/electromagnetic-waves) are focused into a narrow cone.\nDimensions are small in comparison to the wavelength and thus the slab behaves as a homogeneous material with a low [plasma frequency](https://bliptext.com/articles/plasma-frequency).\n\n# Transmission line models\n\n## Conventional transmission lines\nA [transmission line](https://bliptext.com/articles/[transmission](https://bliptext.com/articles/transmission-telecommunications)-line) is the material [medium](https://bliptext.com/articles/[transmission](https://bliptext.com/articles/transmission-telecommunications)-medium) or structure that forms all or part of a [path](https://bliptext.com/articles/course-navigation) from one place to another for directing the [transmission](https://bliptext.com/articles/transmission-telecommunications) of energy, such as [electromagnetic waves](https://bliptext.com/articles/electromagnetic-wave) or electric power [transmission](https://bliptext.com/articles/transmission-telecommunications).\nTypes of transmission line include [wires](https://bliptext.com/articles/wire), [coaxial cables](https://bliptext.com/articles/coaxial-cable), dielectric slabs, [striplines](https://bliptext.com/articles/stripline), [optical fibers](https://bliptext.com/articles/optical-fiber), [electric power lines](https://bliptext.com/articles/power-line) and waveguides.\nA [microstrip](https://bliptext.com/articles/microstrip) is a type of transmission line that can be fabricated using [printed circuit board](https://bliptext.com/articles/printed-circuit-board) technology and is used to convey microwave-frequency signals.\nIt consists of a conducting strip separated from a ground plane by a dielectric layer known as the **substrate**.\nMicrowave components such as [antennas](https://bliptext.com/articles/microstrip-antenna), [couplers](https://bliptext.com/articles/directional-coupler), [filters](https://bliptext.com/articles/electronic-filter) and [power dividers](https://bliptext.com/articles/power-dividers-and-directional-couplers) can be formed from a microstrip.\nFrom the simplified schematics to the right it can be seen that total impedance, conductance, reactance (capacitance and inductance) and the transmission medium (transmission line) can be represented by single components that give the overall value.\nWith transmission line media it is important to match the load impedance ZL to the [characteristic impedance](https://bliptext.com/articles/characteristic-impedance) Z0 as closely as possible, because it is usually desirable that the load absorbs as much power as possible.\n# [Variations on the schematic electronic symbol for a transmission line. | upload.wikimedia.org/wikipedia/commons/4/4d/Transmission///line///symbols.svg]\n# [Schematic representation of the elementary components of a transmission line. | upload.wikimedia.org/wikipedia/commons/1/11/Transmission///line///element.svg]\n\n### Lumped circuit elements\nOften, because of the goal that moves physical metamaterial inclusions (or cells) to smaller sizes, discussion and implementation of [lumped LC circuits](https://bliptext.com/articles/lumped-element-model) or [distributed LC networks](https://bliptext.com/articles/distributed-element-model) are often examined.\nLumped circuit elements are actually microscopic elements that effectively approximate their larger component counterparts.\nFor example, circuit capacitance and inductance can be created with split rings, which are on the scale of nanometers at optical frequencies.\nThe distributed LC model is related to the lumped LC model, however the [distributed-element model](https://bliptext.com/articles/distributed-element-model) is more accurate but more complex than the [lumped-element model](https://bliptext.com/articles/lumped-element-model).\n\n## Metamaterial-loaded transmission-line configurations\nSome noted metamaterial antennas employ negative-refractive-index transmission-line metamaterials (NRI-TLM).\nThese include [lenses](https://bliptext.com/articles/lens-optics) that can overcome the [diffraction](https://bliptext.com/articles/diffraction) limit, narrowband and broadband phase-shifting lines, small antennas, low-profile antennas, antenna feed networks, novel power architectures, and high-directivity couplers.\nLoading a planar metamaterial network of TLs with series capacitors and shunt inductors produces higher performance.\nThis results in a large operating [bandwidth](https://bliptext.com/articles/bandwidth-signal-processing) while the refractive index is negative.\nBecause [superlenses](https://bliptext.com/articles/superlens) can overcome the [diffraction limit](https://bliptext.com/articles/diffraction-limit), this allows for a more efficient coupling to external radiation and enables a broader frequency band.\nFor example, the superlens can be applied to the TLM architecture.\nIn conventional lenses, imaging is limited by the [diffraction limit](https://bliptext.com/articles/diffraction-limit).\nWith superlenses the details of the [near field](https://bliptext.com/articles/near-and-far-field) images are not lost.\nGrowing [evanescent waves](https://bliptext.com/articles/evanescent-waves) are supported in the metamaterial (n < 1), which restores the decaying [evanescent waves](https://bliptext.com/articles/evanescent-waves) from the source.\nThis results in a diffraction-limited resolution of λ/6, after some small losses.\nThis compares with λ/2, the normal diffraction limit for conventional [lenses](https://bliptext.com/articles/microwave-lens).\nBy combining right-handed (RHM) with left-handed materials (LHM) as a composite material (CRLH) construction, both a backward to forward [scanning](https://bliptext.com/articles/radar) capability is obtained.\nMetamaterials were first used for antenna technology around 2005.\nThis type of antenna used the established capability of SNGs to couple with external [radiation](https://bliptext.com/articles/radiation).\nResonant [coupling](https://bliptext.com/articles/coupling) allowed for a wavelength larger than the antenna.\nAt microwave frequencies this allowed for a smaller antenna.\nA metamaterial-loaded transmission line has significant advantages over conventional or standard delay transmission lines.\nIt is more compact in size, it can achieve positive or negative [phase shift](https://bliptext.com/articles/phase-shift) while occupying the same short physical length and it exhibits a linear, flatter [phase response](https://bliptext.com/articles/phase-response) with [frequency](https://bliptext.com/articles/frequency), leading to shorter group delays.\nIt can work in lower frequency because of high series distributed-capacitors and has smaller plane dimensions than its equivalent coplanar structure.\n\n### Negative refractive index metamaterials supporting 2-D waves\nIn 2002, rather than using SRR-wire configuration, or other 3-D media, researchers looked at planar configurations that supported backward wave propagation, thus demonstrating negative refractive index and focusing as a consequence.\nIt has long been known that transmission lines [periodically](https://bliptext.com/articles/periodic-function) loaded with capacitive and inductive elements in a high-pass configuration support certain types of backward waves.\nIn addition, planar transmission lines are a natural match for 2-D wave propagation.\nWith lumped circuit elements they retain a compact configuration and can still support the lower RF range.\nWith this in mind, high pass and cutoff, periodically loaded, two-dimensional LC transmission line networks were proposed.\nThe LC networks can be designed to support backward waves, without bulky SRR/wire structure.\nThis was the first such proposal which veered away from bulk media for a negative refractive effect.\nA notable property of this type of network is that there is no reliance on resonance, Instead the ability to support backward waves defines negative refraction.\nThe principles behind focusing are derived from Veselago and Pendry.\nCombining a conventional, flat, (planar) DPS slab, M-1, with a left-handed medium, M-2, a propagating electromagnetic wave with a [wave vector](https://bliptext.com/articles/wave-vector) k1 in M-1, results in a refracted wave with a [wave vector](https://bliptext.com/articles/wave-vector) k2 in M-2.\nSince, M-2 supports backward wave propagation k2 is refracted to the opposite side of the normal, while the [Poynting vector](https://bliptext.com/articles/poynting-vector) of M-2 is anti-parallel with k2.\nUnder such conditions, power is refracted through an effectively negative angle, which implies an effectively negative index of refraction.\nElectromagnetic waves from a point source located inside a conventional DPS can be focused inside an LHM using a planar interface of the two media.\nThese conditions can be modeled by exciting a single node inside the DPS and observing the magnitude and phase of the voltages to ground at all points in the LHM.\nA focusing effect should manifest itself as a “spot” distribution of voltage at a predictable location in the LHM.\nNegative refraction and focusing can be accomplished without employing resonances or directly synthesizing the permittivity and permeability.\nIn addition, this media can be practically fabricated by appropriately loading a host transmission line medium.\nFurthermore, the resulting planar topology permits LHM structures to be readily integrated with conventional planar microwave circuits and devices.\nWhen transverse electromagnetic propagation occurs with a transmission line medium, the analogy for permittivity and permeability is ε = L, and μ = C. This analogy was developed with positive values for these parameters.\nThe next logic step was realizing that negative values could be achieved.\nIn order to synthesize a left-handed medium (ε < 0 and μ < 0) the series reactance and shunt susceptibility should become negative, because the material parameters are directly proportional to these circuit quantities.\nA transmission line that has lumped circuit elements that synthesize a left-handed medium is referred to as a \"dual transmission line\" as compared to \"conventional transmission line\".\nThe dual transmission line structure can be implemented in practice by loading a host transmission line with lumped series capacitors (C) and shunt inductors (L).\nIn this periodic structure, the loading is strong such that the lumped elements dominate the propagation characteristics.\n\n### Left-handed behavior in LC loaded transmission lines\nUsing SRRs at [RF frequencies](https://bliptext.com/articles/radio-frequency), as with wireless devices, requires the resonators to be scaled to larger dimensions.\nThis worked against making the devices more compact.\nIn contrast, [LC network](https://bliptext.com/articles/tank-circuit) configurations could be scaled to both microwave and RF frequencies.\nLC-loaded [transmission lines](https://bliptext.com/articles/transmission-lines) enabled a new class of metamaterials to produce a [negative refractive index](https://bliptext.com/articles/negative-refractive-index).\nRelying on LC networks to emulate electrical [permittivity](https://bliptext.com/articles/permittivity) and [magnetic permeability](https://bliptext.com/articles/magnetic-permeability) resulted in a substantial increase in operating bandwidths.\nMoreover, their unit cells are connected through a transmission-line network and may be equipped with [lumped circuit](https://bliptext.com/articles/lumped-circuit) elements, which permit them to be compact at frequencies where an SRR cannot be compact.\nThe flexibility gained through the use of either discrete or printed elements enables planar metamaterials to be scalable from the [megahertz](https://bliptext.com/articles/megahertz) to the [tens of gigahertz](https://bliptext.com/articles/gigahertz) range.\nIn addition, replacing capacitors with [varactors](https://bliptext.com/articles/varactor) allowed the material properties to be dynamically tuned.\nThe proposed media are planar and inherently support two-dimensional (2-D) wave propagation, making them well-suited for RF/microwave device and circuit applications.\n\n### Growing evanescent waves in negative-refractive-index transmission-line media\nThe periodic 2-D LC loaded transmission-line (TL) was shown to exhibit NRI properties over a broad frequency range.\nThis network will be referred to as a dual TL structure since it is of a high-pass configuration, as opposed to the low-pass representation of a conventional TL structure.\nDual TL structures have been used to experimentally demonstrate backward-wave radiation and focusing at microwave frequencies.\nAs a negative refractive index medium, a dual TL structure is not simply a phase compensator.\nIt can enhance the amplitude of evanescent waves, as well as correct the phase of propagating waves.\nEvanescent waves actually grow within the dual TL structure.\n\n### Backward wave antenna using an NRI loaded transmission line\nGrbic et al. used one-dimensional LC loaded transmission line network, which supports fast backward-wave propagation to demonstrate characteristics analogous to \"reversed Cherenkov radiation\".\nTheir proposed backward-wave radiating structure was inspired by negative refractive index LC materials.\nThe simulated E-plane pattern at 15 GHz showed radiation towards the backfire direction in the far-field pattern, clearly indicating the excitation of a backward wave.\nSince the transverse dimension of the array is electrically short, the structure is backed by a long metallic trough.\nThe trough acts as a waveguide below cut-off and recovers the back radiation, resulting in unidirectional far-field patterns.\n\n### Planar NIMs with periodic loaded transmission lines\nPlanar media can be implemented with an effective negative refractive index.\nThe underlying concept is based on appropriately loading a printed network of transmission lines periodically with inductors and capacitors.\nThis technique results in effective permittivity and permeability material parameters that are both inherently and simultaneously negative, obviating the need to employ separate means.\nThe proposed media possess other desirable features including very wide bandwidth over which the refractive index remains negative, the ability to guide 2-D TM waves, scalability from RF to millimeter-wave frequencies and low transmission losses, as well as the potential for tunability by inserting varactors and/or switches in the unit cell.\nThe concept has been verified with circuit and full-wave simulations.\nA prototype focusing device has been tested experimentally.\nThe experimental results demonstrated focusing of an incident cylindrical wave within an octave bandwidth and over an electrically short area; suggestive of near-field focusing.\nRF/microwave devices can be implemented based on these proposed media for applications in wireless communications, surveillance and radars.\n\n## Larger transmission lines\nAccording to some researchers SRR/wire-configured metamaterials are bulky 3-D constructions that are difficult to adapt for RF/microwave device and circuit applications.\nThese structures can achieve a negative index of refraction only within a narrow bandwidth.\nWhen applied to wireless devices at RF frequencies the split ring-resonators have to be scaled to larger dimensions, which, in turn forces a larger device size.\nThe proposed structures go beyond the wire/SRR composites in that they do not rely on SRRs to synthesize the material parameters, thus leading to dramatically increased operating bandwidths.\nMoreover, their unit cells are connected through a transmission-line network and they may, therefore, be equipped with lumped elements, which permit them to be compact at frequencies where the SRR cannot be compact.\nThe flexibility gained through the use of either discrete or printed elements enables planar metamaterials to be scalable from the megahertz to the tens of gigahertz range.\nIn addition, by utilizing varactors instead of capacitors, the effective material properties can be dynamically tuned.\nFurthermore, the proposed media are planar and inherently support two-dimensional (2-D) wave propagation.\nTherefore, these new metamaterials are well suited for RF/microwave device and circuit applications.\nIn the long-wavelength regime, the permittivity and permeability of conventional materials can be artificially synthesized using periodic LC networks arranged in a low-pass configuration.\nIn the dual (high-pass) configuration, these equivalent material parameters assume simultaneously negative values, and may therefore be used to synthesize a negative refractive index.\n\n# Configurations\nAntenna theory is based on [classical electromagnetic theory](https://bliptext.com/articles/classical-electromagnetism) as described by [Maxwell's equations](https://bliptext.com/articles/maxwell-s-equations).\nPhysically, an antenna is an arrangement of one or more [conductors](https://bliptext.com/articles/electrical-conductor), usually called elements.\nAn [alternating current](https://bliptext.com/articles/alternating-current) is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field.\nIn reception, the reverse occurs: an electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna's terminals.\nSome receiving antennas (such as parabolic and horn types) incorporate shaped reflective surfaces to collect EM waves from free space and direct or focus them onto the actual conductive elements.\nAn antenna creates sufficiently strong electromagnetic fields at large distances.\nReciprocally, it is sensitive to the electromagnetic fields impressed upon it externally.\nThe actual coupling between a transmitting and receiving antenna is so small that amplifier circuits are required at both the transmitting and receiving stations.\nAntennas are usually created by modifying ordinary circuitry into transmission line configurations.\nThe required antenna for any given application is dependent on the bandwidth employed, and range (power) requirements.\nIn the microwave to millimeter-wave range – wavelengths from a few meters to millimeters – the following antennas are usually employed:\nDipole antennas, short antennas, parabolic and other reflector antennas, horn antennas, periscope antennas, helical antennas, spiral antennas, surface-wave and leaky wave antennas.\nLeaky wave antennas include dielectric and dielectric loaded antennas, and the variety of microstrip antennas.\n\n## Radiation properties with SRRs\nThe SRR was introduced by Pendry in 1999, and is one of the most common elements of [metamaterials](https://bliptext.com/articles/metamaterial).\nAs a nonmagnetic conducting unit, it comprises an array of units that yield an enhanced negative effective magnetic permeability, when the frequency of the incident electromagnetic field is close to the SRR resonance frequency.\nThe resonant frequency of the SRR depends on its shape and physical design.\nIn addition, resonance can occur at wavelengths much larger than its size.\nFor the further shape optimization of the elements it is expedient to use genetic and other optimization algorithms.\nIn multi-frequency designs one may apply fractal designs such as those of Sierpensky, Koch or other fractals instead of SRRs.\n\n### Double negative metamaterials\nThrough the application of [double negative metamaterials](https://bliptext.com/articles/double-negative-metamaterial) (DNG), the [power radiated](https://bliptext.com/articles/power-physics) by [electrically](https://bliptext.com/articles/electromagnetism) small [dipole](https://bliptext.com/articles/dipole) antennas can be notably increased.\nThis could be accomplished by surrounding an antenna with a shell of double negative (DNG) material.\nWhen the electric dipole is embedded in a [homogeneous](https://bliptext.com/articles/homogeneity-physics) DNG medium, the antenna acts inductively rather than capacitively, as it would in [free space](https://bliptext.com/articles/free-space) without the interaction of the DNG material.\nIn addition, the dipole-DNG shell combination increases the real power radiated by more than an [order of magnitude](https://bliptext.com/articles/order-of-magnitude) over a free space antenna.\nA notable decrease in the reactance of the dipole antenna corresponds to the increase in radiated power.\nThe reactive power indicates that the DNG shell acts as a natural matching network for the dipole.\nThe DNG material matches the intrinsic reactance of this antenna system to free space, hence the impedance of DNG material matches free space.\nIt provides a natural matching circuit to the antenna.\n\n### Single negative SRR and monopole composite\nThe addition of an [SRR-DNG metamaterial](https://bliptext.com/articles/split-ring-resonator) increased the [radiated power](https://bliptext.com/articles/power-physics) by more than an [order of magnitude](https://bliptext.com/articles/order-of-magnitude) over a comparable free space antenna.\nElectrically small antennas, high [directivity](https://bliptext.com/articles/directivity) and tunable operational frequency are produced with negative magnetic permeability.\nWhen combining a right-handed material (RHM) with a Veselago-left-handed material (LHM) other novel properties are obtained.\nA single negative material resonator, obtained with an SRR, can produce an electrically small antenna when operating at microwave frequencies, as follows:\nThe configuration of an SRR assessed was two concentric [annular](https://bliptext.com/articles/annulus-mathematics) rings with relative opposite gaps in the inner and outer ring.\nIts [geometrical](https://bliptext.com/articles/geometrical) parameters were R = 3.6 mm, r = 2.5 mm, w = 0.2 mm, t = 0.9 mm. R and r are used in annular parameters, w is the spacing between the rings and t = the width of the outer ring.\nThe material had a thickness of 1.6 mm. Permittivity was 3.85 at 4 GHz.\nThe SRR was fabricated with an etching technique onto a 30 [μm](https://bliptext.com/articles/m) thick [copper](https://bliptext.com/articles/copper) substrate.\nThe SRR was excited by using a [monopole antenna](https://bliptext.com/articles/monopole-antenna).\nThe monopole antenna was composed of a [coaxial cable](https://bliptext.com/articles/coaxial-cable), ground plane and radiating components.\nThe ground plane material was [aluminium](https://bliptext.com/articles/aluminium).\nThe operation frequency of the antenna was 3.52 GHz, which was determined by considering the geometrical parameters of SRR.\nAn 8.32 mm length of wire was placed above the ground plane, connected to the antenna, which was one quarter of the operation wavelength.\nThe antenna worked with a feed wavelength of 3.28 mm and feed frequency of 7.8 GHz.\nThe SRR's resonant frequency was smaller than the monopole operation frequency.\nThe monopole-SRR antenna operated efficiently at (λ/10) using the SRR-wire configuration.\nIt demonstrated good coupling efficiency and sufficient radiation efficiency.\nIts operation was comparable to a conventional antenna at λ/2, which is a conventional antenna size for efficient coupling and radiation.\nTherefore, the monopole-SRR antenna becomes an acceptable electrically small antenna at the SRR's resonance frequency.\nWhen the SRR is made part of this configuration, characteristics such as the antenna's radiation pattern are entirely changed in comparison to a conventional monopole antenna.\nWith modifications to the SRR structure the antenna size could reach (**λ/40**).\nCoupling 2, 3, and 4 SRRs side by side slightly shifts radiation patterns.\n\n## Patch antennas\nIn 2005 a [patch antenna](https://bliptext.com/articles/patch-antenna) with a [metamaterial cover](https://bliptext.com/articles/metamaterial-cover) was proposed that enhanced [directivity](https://bliptext.com/articles/directivity).\nAccording to the numerical results, the antenna showed significant improvement in directivity, compared to conventional patch antennae.\nThis was cited in 2007 for an efficient design of directive patch antennas in mobile communications using metamaterials.\nThis design was based on the left-handed material (LHM) transmission line model, with the circuit elements L and C of the LHM [equivalent circuit](https://bliptext.com/articles/equivalent-circuit) model.\nThis study developed [formulae](https://bliptext.com/articles/formula) to determine the L and C values of the LHM equivalent circuit model for desirable characteristics of directive patch antennas.\nDesign examples derived from actual [frequency](https://bliptext.com/articles/frequency) bands in [mobile communications](https://bliptext.com/articles/mobile-communications) were performed, which illustrates the efficiency of this approach.\n\n## Flat lens horn antenna\nThis configuration uses a flat aperture constructed of zero-index metamaterial.\nThis has advantages over ordinary (conventional) curved lenses, which results in a much improved directivity.\nThese investigations have provided capabilities for the miniaturization of microwave source and non-source devices, circuits, antennas and the improvement of electromagnetic performance.\n\n## Metamaterials surface antenna technology\n**Metamaterials surface antenna technology** (M-SAT) is an invention that uses metamaterials to direct and maintain a consistent broadband [radio frequency](https://bliptext.com/articles/radio-frequency) beam locked on to a [satellite](https://bliptext.com/articles/satellite) whether the platform is in motion or stationary.\n[Gimbals](https://bliptext.com/articles/gimbal) and motors are replaced by arrays of metamaterials in a planar configuration.\nAlso, with this new technology [phase shifters](https://bliptext.com/articles/phase-shifter) are not required as with [phased array](https://bliptext.com/articles/phased-array) equipment.\nThe desired affect is accomplished by varying the pattern of activated metamaterial elements as needed.\nThe technology is a practical application of [metamaterial cloaking](https://bliptext.com/articles/metamaterial-cloaking) theory.\nThe antenna is approximately the size of a laptop computer.\nResearch and applications of metamaterial based antennas.\nRelated components are also researched.\n\n# Subwavelength cavities and waveguides\nWhen the interface between a pair of materials that function as optical [transmission media](https://bliptext.com/articles/transmission-media) interact as a result of opposing permittivity and / or permeability values that are either ordinary (positive) or extraordinary (negative), notable anomalous behaviors may occur.\nThe pair would be a DNG metamaterial (layer), paired with a DPS, ENG or MNG layer.\nWave propagation behavior and properties may occur that would otherwise not happen if only DNG layers are paired together.\nAt the interface between two media, the concept of the continuity of the tangential electric and magnetic field components can be applied.\nIf either the permeability or permittivity of two media has opposite signs then the normal components of the tangential field, on both sides of the interface, will be discontinuous at the boundary.\nThis implies a concentrated resonant phenomenon at the interface.\nThis appears to be similar to the current and voltage distributions at the junction between an inductor and capacitor, at the resonance of an L-C circuit.\nThis \"interface resonance\" is essentially independent of the total thickness of the paired layers, because it occurs along the discontinuity between two such conjugate materials.\n\n## Parallel-plate waveguiding structures\nThe geometry consists of two parallel plates as perfect conductors (PEC), an idealized structure, filled by two stacked planar slabs of homogeneous and isotropic materials with their respective constitutive parameters ε1, ε2, u1, u2.\nEach slab has thickness = d, slab 1 = d1, and slab 2 = d2.\nChoosing which combination of parameters to employ involves pairing DPS and DNG or ENG and MNG materials.\nAs mentioned previously, this is one pair of oppositely-signed constitutive parameters, combined.\n\n## Thin subwavelength cavity resonators\n\n### Phase compensation\nThe real component values for negative permittivity and permeability results in real component values for negative refraction n. In a lossless medium, all that would exist are real values.\nThis concept can be used to map out phase compensation when a conventional lossless material, DPS, is matched with a lossless NIM (DNG).\nIn phase compensation, the DPS of thickness d1 has ε > 0 and μ > 0.\nConversely, the NIM of thickness d2 has ε < 0 and μ < 0.\nAssume that the intrinsic impedance of the DPS dielectric material (d1) is the same as that of the outside region and responding to a normally incident planar wave.\nThe wave travels through the medium without any reflection because the DPS impedance and the outside impedance are equal.\nHowever, the plane wave at the end of DPS slab is out of phase with the plane wave at the beginning of the material.\nThe plane wave then enters the lossless NIM (d2).\nAt certain frequencies ε < 0 and μ < 0 and n < 0.\nLike the DPS, the NIM has intrinsic impedance that is equal to the outside, and, therefore, is also lossless.\nThe direction of power flow (i.e., the Poynting vector) in the first slab should be the same as that in the second one, because the power of the incident wave enters the first slab (without any reflection at the first interface), traverses the first slab, exits the second interface, enters the second slab and traverses it, and finally leaves the second slab.\nHowever, as stated earlier, the direction of power is anti-parallel to the direction of phase velocity.\nTherefore, the wave vector k2 is in the opposite direction of k1.\nFurthermore, whatever phase difference is developed by traversing the first slab can be decreased and even cancelled by traversing the second slab.\nIf the ratio of the two thicknesses is **d1 / d2 = n2 / n1**, then the total phase difference between the front and back faces is zero.\nThis demonstrates how the NIM slab at chosen frequencies acts as a phase compensator.\nIt is important to note that this phase compensation process is only on the ratio of **d1 / d2** rather than the thickness of **d1 + d1**.\nTherefore, **d1 + d1** can be any value, as long as this ratio satisfies the above condition.\nFinally, even though this two-layer structure is present, the wave traversing this structure would not experience the phase difference.\nFollowing this, the next step is the subwavelength cavity resonator.\n\n### Compact subwavelength 1-D cavity resonators using metamaterials\nThe phase compensator described above can be used to conceptualize the possibility of designing a compact 1-D cavity resonator.\nThe above two-layer structure is applied as two perfect\nreflectors, or in other words, two perfect conducting plates.\nConceptually, what is constrained in the resonator is **d1 / d2**, not **d1 + d2**.\nTherefore, in principle, one can have a thin subwavelength cavity resonator for a given frequency, if at this frequency the second layer acts a metamaterial with negative permittivity and permeability and the ratio correlates to the correct values.\nThe cavity can conceptually be thin while still resonant, as long as the ratio of thicknesses is satisfied.\nThis can, in principle, provide possibility for subwavelength, thin, compact cavity resonators.\n\n## Miniature cavity resonator utilizing FSS\nFrequency selective surface (FSS) based metamaterials utilize equivalent LC circuitry configurations.\nUsing FSS in a cavity allows for miniaturization, decrease of the resonant frequency, lowers the cut-off frequency and smooth transition from a fast-wave to a slow-wave in a waveguide configuration.\n\n## Composite metamaterial based cavities\nAs an LHM application four different cavities operating in the microwave regime were fabricated and experimentally observed and described.\n\n# Metamaterial ground plane\n\n## Leaky mode propagation with metamaterial ground plane\nA magnetic dipole was placed on metamaterial (slab) ground plane.\nThe metamaterials have either constituent parameters that are both negative, or negative permittivity or negative permeability.\nThe dispersion and radiation properties of leaky waves supported by these metamaterial slabs, respectively, were investigated.\n\n# Patented systems\nMultiple systems have [patents](https://bliptext.com/articles/patent).\nPhased array systems and antennas for use in such systems are well known in areas such as telecommunications and [radar](https://bliptext.com/articles/radar) applications.\nIn general phased array systems work by coherently reassembling signals over the entire array by using circuit elements to compensate for relative phase differences and time delays.\n# [Microstrip line (400) for a phased array metamaterial antenna system. 401 represents unit-cell circuits composed periodically along the microstrip. 402 series capacitors. 403 are T-junctions between capacitors, which connect (404) spiral inductor delay lines to 401. 404 are also connected to ground vias 405. | upload.wikimedia.org/wikipedia/commons/0/0d/Phased///array///metamaterial///system.jpg]\n\n## Phased array antenna\nPatented in 2004, one phased array antenna system is useful in automotive radar applications.\nBy using NIMs as a [biconcave lens](https://bliptext.com/articles/biconcave-lens) to focus microwaves, the antenna's [sidelobes](https://bliptext.com/articles/sidelobe) are reduced in size.\nThis equates to a reduction in radiated energy loss, and a relatively wider useful bandwidth.\nThe system is an efficient, dynamically ranged [phased array radar](https://bliptext.com/articles/phased-array-radar) system.\nIn addition, signal amplitude is increased across the [microstrip](https://bliptext.com/articles/microstrip) transmission lines by suspending them above the ground plane at a predetermined distance.\nIn other words, they are not in contact with a solid substrate.\nDielectric signal loss is reduced significantly, reducing signal attenuation.\nThis system was designed to boost the performance of the [Monolithic microwave integrated circuit](https://bliptext.com/articles/monolithic-microwave-integrated-circuit) (MMIC), among other benefits.\nA transmission line is created with photolithography.\nA metamaterial lens, consisting of a thin wire array focuses the transmitted or received signals between the line and the emitter / receiver elements.\nThe lens also functions as an input device and consists of a number of periodic unit-cells disposed along the line.\nThe lens consists of multiple lines of the same make up; a plurality of periodic unit-cells.\nThe periodic unit-cells are constructed of a plurality of electrical components; capacitors and inductors as components of multiple [distributed-element circuits](https://bliptext.com/articles/distributed-element-circuit).\nThe metamaterial incorporates a conducting [transmission element](https://bliptext.com/articles/transmission-medium), a substrate comprising at least a first ground plane for grounding the [transmission element](https://bliptext.com/articles/transmission-medium), a plurality of unit-cell circuits composed periodically along the [transmission element](https://bliptext.com/articles/transmission-medium) and at least one [via](https://bliptext.com/articles/via-electronics) for electrically connecting the [transmission element](https://bliptext.com/articles/transmission-medium) to at least the first ground plane.\nIt also includes a means for suspending this transmission element a predetermined distance from the substrate in a way such that the transmission element is located at a second predetermined distance from the ground plane.\n\n## ENG and MNG waveguides and scattering devices\nThis structure was designed for use in waveguiding or scattering of waves.\nIt employs two adjacent layers.\nThe first layer is an epsilon-negative (ENG) material or a mu-negative (MNG) material.\nThe second layer is either a double-positive (DPS) material or a double-negative (DNG) material.\nAlternatively, the second layer can be an ENG material when the first layer is an MNG material or the reverse.\n\n# Reducing interference\nMetamaterials can reduce interference across multiple devices with smaller and simpler shielding.\nWhile conventional absorbers can be three inches thick, metamaterials can be in the millimeter range—2 mm (0.078 in) thick.\n# [A keyless entry system key fob | upload.wikimedia.org/wikipedia/commons/a/a4/SundryKeyFobs2154.jpg]\n\n## General references","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-26T12:06:28.720Z","updated_at":"2025-01-26T12:06:28.720Z","search_vector":"'antenna':2 'metamateri':1","search_content":" \n \n\n# \n**Metamaterial [antennas](https://bliptext.com/articles/antenna-radio)** are a class of [antennas](https://bliptext.com/articles/antenna-radio) which use [metamaterials](https://bliptext.com/articles/metamaterials) to increase performance of miniaturized ([electrically small](https://bliptext.com/articles/electrically-small-antenna)) [antenna systems](https://bliptext.com/articles/antenna-radio).\nTheir purpose, as with any electromagnetic antenna, is to launch [energy](https://bliptext.com/articles/energy) into free space.\nHowever, this class of antenna incorporates metamaterials, which are materials engineered with novel, often [microscopic](https://bliptext.com/articles/microscopic), structures to produce unusual [physical properties](https://bliptext.com/articles/physical-properties).\nAntenna designs incorporating metamaterials can step-up the antenna's radiated [power](https://bliptext.com/articles/power-physics).\nConventional antennas that are very small compared to the [wavelength](https://bliptext.com/articles/wavelength) reflect most of the signal back to the source.\nA metamaterial antenna behaves as if it were much larger than its actual size, because its novel structure stores and re-radiates energy.\nEstablished lithography techniques can be used to print metamaterial elements on a [printed circuit board](https://bliptext.com/articles/printed-circuit-board).\nThese novel antennas aid applications such as portable interaction with satellites, wide angle beam steering, emergency communications devices, [micro-sensors](https://bliptext.com/articles/sensor) and portable [ground-penetrating radars](https://bliptext.com/articles/radar) to search for geophysical features.\nSome applications for metamaterial antennas are [wireless communication](https://bliptext.com/articles/wireless-communication), [space communications](https://bliptext.com/articles/space-communications-and-navigation-program), [GPS](https://bliptext.com/articles/gps), [satellites](https://bliptext.com/articles/satellite), space vehicle navigation and airplanes.\n# [This Z antenna tested at the National Institute of Standards and Technology is smaller than a standard antenna with comparable properties. Its high efficiency is derived from the \"Z element\" inside the square that acts as a metamaterial, greatly boosting the radiated signal. The square is 30 millimeters on a side. | upload.wikimedia.org/wikipedia/commons/6/63/Z///Antennas///at///UHF///Frequencies.jpg]\n\n# Antennas designs\nAntenna designs incorporating metamaterials can step-up the radiated [power](https://bliptext.com/articles/power-physics) of an antenna.\nThe newest metamaterial antennas radiate as much as 95 percent of an input [radio signal](https://bliptext.com/articles/radio-signal).\nStandard antennas need to be at least half the size of the signal wavelength to operate efficiently.\nAt [300 MHz](https://bliptext.com/articles/megahertz), for instance, an antenna would need to be half a meter long.\nIn contrast, experimental metamaterial antennas are as small as one-fiftieth of a wavelength, and could have further decreases in size.\nMetamaterials are a basis for further miniaturization of [microwave antennas](https://bliptext.com/articles/microwave-antenna), with efficient power and acceptable bandwidth.\nAntennas employing metamaterials offer the possibility of overcoming restrictive efficiency-bandwidth limitations for conventionally constructed, miniature antennas.\nMetamaterials permit smaller antenna elements that cover a wider [frequency range](https://bliptext.com/articles/frequency-range), thus making better use of available space for space-constrained cases.\nIn these instances, miniature antennas with high gain are significantly relevant because the radiating elements are combined into large antenna arrays.\nFurthermore, metamaterials' negative [refractive index](https://bliptext.com/articles/refractive-index) focuses [electromagnetic radiation](https://bliptext.com/articles/electromagnetic-radiation) by a [flat lens](https://bliptext.com/articles/flat-lens) versus being dispersed.\n\n## The DNG shell\nThe earliest research in metamaterial antennas was an analytical study of a miniature dipole antenna surrounded with a metamaterial.\nThis material is known variously as a negative index metamaterial (NIM) or double negative metamaterial (DNG) among other names.\nThis configuration analytically and numerically appears to produce an order of magnitude increase in power.\nAt the same time, the reactance appears to offer a corresponding decrease.\nFurthermore, the DNG shell becomes a natural impedance matching network for this system.\n\n# Ground plane applications\nMetamaterials employed in the [ground planes](https://bliptext.com/articles/ground-plane) surrounding antennas offer improved isolation between [radio frequency](https://bliptext.com/articles/radio-frequency), or [microwave](https://bliptext.com/articles/microwave) channels of ([multiple-input multiple-output](https://bliptext.com/articles/multiple-input-multiple-output)) (MIMO) [antenna arrays](https://bliptext.com/articles/phased-array).\nMetamaterial, [high-impedance groundplanes](https://bliptext.com/articles/tunable-metamaterials) can also improve [radiation](https://bliptext.com/articles/radio-frequency) efficiency and axial ratio performance of low-profile antennas located close to the [ground plane surface](https://bliptext.com/articles/ground-plane).\nMetamaterials have also been used to increase [beam scanning](https://bliptext.com/articles/microwave-scanning-beam-landing-system) range by using both the forward and backward waves in leaky wave antennas.\nVarious metamaterial antenna systems can be employed to support surveillance sensors, communication links, navigation systems and command and control systems.\n\n# Novel configurations\nBesides antenna miniaturization, the novel configurations have potential applications ranging from radio frequency devices to optical devices.\nOther combinations, for other devices in metamaterial antenna subsystems are being researched.\nEither [double negative metamaterial](https://bliptext.com/articles/double-negative-metamaterial) slabs are used exclusively or combinations of [double positive (DPS)](https://bliptext.com/articles/metamaterial) with DNG slabs, or [epsilon-negative (ENG)](https://bliptext.com/articles/metamaterial) slabs with [mu-negative (MNG)](https://bliptext.com/articles/metamaterial) slabs are employed in the subsystems.\nAntenna subsystems that are currently being researched include [cavity resonators](https://bliptext.com/articles/resonator), waveguides, scatters and antennas (radiators).\nMetamaterial antennas were commercially available by 2009.\n\n# History\n[Pendry](https://bliptext.com/articles/pendry) et al. were able to show that a three-[dimensional](https://bliptext.com/articles/dimension) array of intersecting, thin wires could be used to create negative values of [permittivity](https://bliptext.com/articles/permittivity) (\"**ε**\"), and that a periodic array of copper split ring resonators could produce an effective negative [magnetic permeability](https://bliptext.com/articles/magnetic-permeability) ( \"**μ**\").\nIn May 2000, a group of researchers, Smith et al. were the first to successfully combine the [split-ring resonator](https://bliptext.com/articles/split-ring-resonator) (SRR), with thin wire conducting posts and produce a [left-handed material](https://bliptext.com/articles/left-handed-material) that had negative values of ε, μ and [refractive index](https://bliptext.com/articles/refractive-index) for frequencies in the [gigahertz](https://bliptext.com/articles/gigahertz) or [microwave](https://bliptext.com/articles/microwave) range.\nIn 2002, a different class of negative refractive index (NRI) metamaterials was introduced that employs periodic [reactive loading](https://bliptext.com/articles/electrical-reactance) of a 2-D [transmission line](https://bliptext.com/articles/transmission-line) as the host [medium](https://bliptext.com/articles/transmission-medium).\nThis configuration used [positive index](https://bliptext.com/articles/index-of-refraction) (DPS) material with negative index material (DNG).\nIt employed a small, planar, [negative-refractive-lens](https://bliptext.com/articles/superlens) interfaced with a positive index, parallel-plate waveguide.\nThis was experimentally verified soon after.\nAlthough some SRR inefficiencies were identified, they continued to be employed as of 2009 for research.\nSRRs have been involved in wide-ranging metamaterial research, including research on metamaterial antennas.\nA more recent view is that by using SRRs as building blocks, the electromagnetic response and associated flexibility is practical and desirable.\n\n## Phase compensation due to negative refraction\nDNG can provide [phase compensation](https://bliptext.com/articles/phase-waves) due to their negative index of refraction.\nThis is accomplished by combining a slab of conventional lossless DPS material with a slab of lossless DNG metamaterial.\nDPS has a conventional positive [index of refraction](https://bliptext.com/articles/index-of-refraction), while the DNG has a negative refractive index.\nBoth slabs are [impedance](https://bliptext.com/articles/impedance-of-free-space)-matched to the outside region (e.g., free space).\nThe desired monochromatic [plane wave](https://bliptext.com/articles/plane-wave) is radiated on this configuration.\nAs this wave propagates through the first slab of material a [phase difference](https://bliptext.com/articles/phase-waves) emerges between the exit and entrance faces.\nAs the wave [propagates](https://bliptext.com/articles/wave-propagation) through the second slab the phase difference is significantly decreased and even compensated for.\nTherefore, as the wave exits the second slab the total phase difference is equal to zero.\nWith this system a phase-compensated, [waveguiding](https://bliptext.com/articles/waveguiding) system could be produced.\nBy stacking slabs of this configuration, the phase compensation (beam translation effects) would occur throughout the entire system.\nFurthermore, by changing the index of any of the DPS-DNG pairs, the speed at which the beam enters the front face, and exits the back face of the entire stack-system changes.\nIn this manner, a volumetric, low loss, time delay [transmission line](https://bliptext.com/articles/transmission-line) could be realized for a given system.\nFurthermore, this phase compensation can lead to a set of applications, which are miniaturized, [subwavelength](https://bliptext.com/articles/subwavelength), [cavity resonators](https://bliptext.com/articles/cavity-resonator), and waveguides with applications below [diffraction limits](https://bliptext.com/articles/diffraction-limit).\n\n## Transmission line dispersion compensation\nBecause of DNG's [dispersive nature](https://bliptext.com/articles/dispersion-relation) as a transmission medium, it could be useful as a dispersion compensation device for [time-domain applications](https://bliptext.com/articles/fourier-transform).\nThe dispersion produces a variance of the [group speed](https://bliptext.com/articles/group-speed) of the signals' wave components, as they propagate in the DNG medium.\nHence, stacked DNG metamaterials could be useful for modifying signal propagation along a [microstrip transmission line](https://bliptext.com/articles/microstrip).\nAt the same time, dispersion leads to distortion.\nHowever, if the dispersion could be compensated for along the microstrip line, [RF](https://bliptext.com/articles/radio-frequency) or microwave signals propagating along them would significantly decrease distortion.\nTherefore, components for attenuating distortion become less critical, and could lead to simplification of many systems.\nMetamaterials can eliminate dispersion along the microstrip by correcting for the frequency dependence of the effective permittivity.\nThe strategy is to design a length of [metamaterial](https://bliptext.com/articles/metamaterial)-loaded transmission line that can be introduced with the original length of [microstrip](https://bliptext.com/articles/microstrip) line to make the paired system [dispersionless](https://bliptext.com/articles/dispersion-optics) creating a dispersion-compensating segment of transmission line.\nThis could be accomplished by introducing a metamaterial with a specific localized [permittivity](https://bliptext.com/articles/permittivity) and a specific localized [magnetic permeability](https://bliptext.com/articles/magnetic-permeability), which then affects the relative [permittivity](https://bliptext.com/articles/permittivity) and permeability of the overall microstrip line.\nIt is introduced so that the wave impedance in the metamaterial remains unchanged.\nThe index of refraction in the medium compensates for the dispersion effects associated with the microstrip geometry itself; making the effective refractive index of the pair that of free space.\nPart of the design strategy is that the effective permittivity and permeability of such a metamaterial should be negative – requiring a DNG material.\n\n## Innovation\nCombining left-handed segments with a conventional (right-handed) transmission line results in advantages over conventional designs.\nLeft-handed transmission lines are essentially a high-pass filter with phase advance.\nConversely, right-handed transmission lines are a low-pass filter with phase lag.\nThis configuration is designated composite right/left-handed (CRLH) metamaterial.\nThe conventional Leaky Wave antenna has had limited commercial success because it lacks complete backfire-to-endfire frequency scanning capability.\nThe CRLH allowed complete backfire-to-endfire frequency scanning, including broadside.\n\n# Microwave lens\nThe [metamaterial lens](https://bliptext.com/articles/metamaterial-lens), found in metamaterial antenna systems, is used as an efficient coupler to external radiation, focusing radiation along or from a [microstrip](https://bliptext.com/articles/microstrip) transmission line into transmitting and receiving components.\nHence, it can be used as an [input device](https://bliptext.com/articles/input-device).\nIn addition, it can enhance the amplitude of [evanescent waves](https://bliptext.com/articles/evanescent-waves), as well as correct the phase of propagating waves.\n\n## Directing radiation\nIn this instance an SRR uses layers of a [metallic](https://bliptext.com/articles/metal) mesh of thin [wires](https://bliptext.com/articles/wire) – with [wires](https://bliptext.com/articles/wire) in the [three directions of space](https://bliptext.com/articles/coordinate-plane) and slices of [foam](https://bliptext.com/articles/foam).\nThis material's permittivity above the [plasma frequency](https://bliptext.com/articles/plasma-frequency) can be positive and less than one.\nThis means that the [refractive index](https://bliptext.com/articles/refractive-index) is just above zero.\nThe relevant parameter is often the contrast between the permittivities rather than the overall permittivity value at desired frequencies.\nThis occurs because the equivalent (effective) permittivity has a behavior governed by a [plasma frequency](https://bliptext.com/articles/plasma-frequency) in the microwave domain.\nThis low optical index material then is a good candidate for extremely convergent [microlenses](https://bliptext.com/articles/microlens).\nMethods that have been developed theoretically using dielectric photonic crystals applied in the microwave domain to realize a directive emitter using metallic grids.\nIn this instance, [arrayed wires in a cubic](https://bliptext.com/articles/crystal-lattice), [crystal lattice](https://bliptext.com/articles/crystal-lattice) structure can be analyzed as an array of aerials ([antenna array](https://bliptext.com/articles/phased-array)).\nAs a lattice structure it has a [lattice constant](https://bliptext.com/articles/lattice-constant).\nThe lattice constant or lattice parameter refers to the constant distance between unit cells in a crystal lattice.\nThe earlier discovery of [plasmons](https://bliptext.com/articles/plasmon) created the view that metal at [plasmon frequency](https://bliptext.com/articles/plasmon-frequency) fp is a composite material.\nThe effect of plasmons on any metal sample is to create properties in the metal such that it can behave as a [dielectric](https://bliptext.com/articles/dielectric), independent of the wave vector of the EM excitation (radiation) field.\nFurthermore, a minute-fractionally small amount of plasmon energy is absorbed into the system denoted as γ.\nFor aluminium fp = 15 eV, and γ = 0.1 eV.\nPerhaps the most important result of the interaction of metal and the plasma frequency is that permittivity is negative below the plasma frequency, all the way to the minute value of γ.\nThese facts ultimately result in the arrayed wire structure as being effectively a homogeneous medium.\nThis metamaterial allows for control of the [direction](https://bliptext.com/articles/polarization-waves) of [emission](https://bliptext.com/articles/emission-electromagnetic-radiation) of an electromagnetic radiation source located inside the material in order to collect all the [energy](https://bliptext.com/articles/energy) in a small angular domain around the [normal](https://bliptext.com/articles/surface-normal).\nBy using a slab of a metamaterial, diverging [electromagnetic waves](https://bliptext.com/articles/electromagnetic-waves) are focused into a narrow cone.\nDimensions are small in comparison to the wavelength and thus the slab behaves as a homogeneous material with a low [plasma frequency](https://bliptext.com/articles/plasma-frequency).\n\n# Transmission line models\n\n## Conventional transmission lines\nA [[transmission](https://bliptext.com/articles/transmission-telecommunications) line](https://bliptext.com/articles/[transmission](https://bliptext.com/articles/transmission-telecommunications)-line) is the material [medium](https://bliptext.com/articles/[transmission](https://bliptext.com/articles/transmission-telecommunications)-medium) or structure that forms all or part of a [path](https://bliptext.com/articles/course-navigation) from one place to another for directing the [transmission](https://bliptext.com/articles/transmission-telecommunications) of energy, such as [electromagnetic waves](https://bliptext.com/articles/electromagnetic-wave) or electric power [transmission](https://bliptext.com/articles/transmission-telecommunications).\nTypes of transmission line include [wires](https://bliptext.com/articles/wire), [coaxial cables](https://bliptext.com/articles/coaxial-cable), dielectric slabs, [striplines](https://bliptext.com/articles/stripline), [optical fibers](https://bliptext.com/articles/optical-fiber), [electric power lines](https://bliptext.com/articles/power-line) and waveguides.\nA [microstrip](https://bliptext.com/articles/microstrip) is a type of transmission line that can be fabricated using [printed circuit board](https://bliptext.com/articles/printed-circuit-board) technology and is used to convey microwave-frequency signals.\nIt consists of a conducting strip separated from a ground plane by a dielectric layer known as the **substrate**.\nMicrowave components such as [antennas](https://bliptext.com/articles/microstrip-antenna), [couplers](https://bliptext.com/articles/directional-coupler), [filters](https://bliptext.com/articles/electronic-filter) and [power dividers](https://bliptext.com/articles/power-dividers-and-directional-couplers) can be formed from a microstrip.\nFrom the simplified schematics to the right it can be seen that total impedance, conductance, reactance (capacitance and inductance) and the transmission medium (transmission line) can be represented by single components that give the overall value.\nWith transmission line media it is important to match the load impedance ZL to the [characteristic impedance](https://bliptext.com/articles/characteristic-impedance) Z0 as closely as possible, because it is usually desirable that the load absorbs as much power as possible.\n# [Variations on the schematic electronic symbol for a transmission line. | upload.wikimedia.org/wikipedia/commons/4/4d/Transmission///line///symbols.svg]\n# [Schematic representation of the elementary components of a transmission line. | upload.wikimedia.org/wikipedia/commons/1/11/Transmission///line///element.svg]\n\n### Lumped circuit elements\nOften, because of the goal that moves physical metamaterial inclusions (or cells) to smaller sizes, discussion and implementation of [lumped LC circuits](https://bliptext.com/articles/lumped-element-model) or [distributed LC networks](https://bliptext.com/articles/distributed-element-model) are often examined.\nLumped circuit elements are actually microscopic elements that effectively approximate their larger component counterparts.\nFor example, circuit capacitance and inductance can be created with split rings, which are on the scale of nanometers at optical frequencies.\nThe distributed LC model is related to the lumped LC model, however the [distributed-element model](https://bliptext.com/articles/distributed-element-model) is more accurate but more complex than the [lumped-element model](https://bliptext.com/articles/lumped-element-model).\n\n## Metamaterial-loaded transmission-line configurations\nSome noted metamaterial antennas employ negative-refractive-index transmission-line metamaterials (NRI-TLM).\nThese include [lenses](https://bliptext.com/articles/lens-optics) that can overcome the [diffraction](https://bliptext.com/articles/diffraction) limit, narrowband and broadband phase-shifting lines, small antennas, low-profile antennas, antenna feed networks, novel power architectures, and high-directivity couplers.\nLoading a planar metamaterial network of TLs with series capacitors and shunt inductors produces higher performance.\nThis results in a large operating [bandwidth](https://bliptext.com/articles/bandwidth-signal-processing) while the refractive index is negative.\nBecause [superlenses](https://bliptext.com/articles/superlens) can overcome the [diffraction limit](https://bliptext.com/articles/diffraction-limit), this allows for a more efficient coupling to external radiation and enables a broader frequency band.\nFor example, the superlens can be applied to the TLM architecture.\nIn conventional lenses, imaging is limited by the [diffraction limit](https://bliptext.com/articles/diffraction-limit).\nWith superlenses the details of the [near field](https://bliptext.com/articles/near-and-far-field) images are not lost.\nGrowing [evanescent waves](https://bliptext.com/articles/evanescent-waves) are supported in the metamaterial (n 0 and μ > 0.\nConversely, the NIM of thickness d2 has ε < 0 and μ < 0.\nAssume that the intrinsic impedance of the DPS dielectric material (d1) is the same as that of the outside region and responding to a normally incident planar wave.\nThe wave travels through the medium without any reflection because the DPS impedance and the outside impedance are equal.\nHowever, the plane wave at the end of DPS slab is out of phase with the plane wave at the beginning of the material.\nThe plane wave then enters the lossless NIM (d2).\nAt certain frequencies ε < 0 and μ < 0 and n < 0.\nLike the DPS, the NIM has intrinsic impedance that is equal to the outside, and, therefore, is also lossless.\nThe direction of power flow (i.e., the Poynting vector) in the first slab should be the same as that in the second one, because the power of the incident wave enters the first slab (without any reflection at the first interface), traverses the first slab, exits the second interface, enters the second slab and traverses it, and finally leaves the second slab.\nHowever, as stated earlier, the direction of power is anti-parallel to the direction of phase velocity.\nTherefore, the wave vector k2 is in the opposite direction of k1.\nFurthermore, whatever phase difference is developed by traversing the first slab can be decreased and even cancelled by traversing the second slab.\nIf the ratio of the two thicknesses is **d1 / d2 = n2 / n1**, then the total phase difference between the front and back faces is zero.\nThis demonstrates how the NIM slab at chosen frequencies acts as a phase compensator.\nIt is important to note that this phase compensation process is only on the ratio of **d1 / d2** rather than the thickness of **d1 + d1**.\nTherefore, **d1 + d1** can be any value, as long as this ratio satisfies the above condition.\nFinally, even though this two-layer structure is present, the wave traversing this structure would not experience the phase difference.\nFollowing this, the next step is the subwavelength cavity resonator.\n\n### Compact subwavelength 1-D cavity resonators using metamaterials\nThe phase compensator described above can be used to conceptualize the possibility of designing a compact 1-D cavity resonator.\nThe above two-layer structure is applied as two perfect\nreflectors, or in other words, two perfect conducting plates.\nConceptually, what is constrained in the resonator is **d1 / d2**, not **d1 + d2**.\nTherefore, in principle, one can have a thin subwavelength cavity resonator for a given frequency, if at this frequency the second layer acts a metamaterial with negative permittivity and permeability and the ratio correlates to the correct values.\nThe cavity can conceptually be thin while still resonant, as long as the ratio of thicknesses is satisfied.\nThis can, in principle, provide possibility for subwavelength, thin, compact cavity resonators.\n\n## Miniature cavity resonator utilizing FSS\nFrequency selective surface (FSS) based metamaterials utilize equivalent LC circuitry configurations.\nUsing FSS in a cavity allows for miniaturization, decrease of the resonant frequency, lowers the cut-off frequency and smooth transition from a fast-wave to a slow-wave in a waveguide configuration.\n\n## Composite metamaterial based cavities\nAs an LHM application four different cavities operating in the microwave regime were fabricated and experimentally observed and described.\n\n# Metamaterial ground plane\n\n## Leaky mode propagation with metamaterial ground plane\nA magnetic dipole was placed on metamaterial (slab) ground plane.\nThe metamaterials have either constituent parameters that are both negative, or negative permittivity or negative permeability.\nThe dispersion and radiation properties of leaky waves supported by these metamaterial slabs, respectively, were investigated.\n\n# Patented systems\nMultiple systems have [patents](https://bliptext.com/articles/patent).\nPhased array systems and antennas for use in such systems are well known in areas such as telecommunications and [radar](https://bliptext.com/articles/radar) applications.\nIn general phased array systems work by coherently reassembling signals over the entire array by using circuit elements to compensate for relative phase differences and time delays.\n# [Microstrip line (400) for a phased array metamaterial antenna system. 401 represents unit-cell circuits composed periodically along the microstrip. 402 series capacitors. 403 are T-junctions between capacitors, which connect (404) spiral inductor delay lines to 401. 404 are also connected to ground vias 405. | upload.wikimedia.org/wikipedia/commons/0/0d/Phased///array///metamaterial///system.jpg]\n\n## Phased array antenna\nPatented in 2004, one phased array antenna system is useful in automotive radar applications.\nBy using NIMs as a [biconcave lens](https://bliptext.com/articles/biconcave-lens) to focus microwaves, the antenna's [sidelobes](https://bliptext.com/articles/sidelobe) are reduced in size.\nThis equates to a reduction in radiated energy loss, and a relatively wider useful bandwidth.\nThe system is an efficient, dynamically ranged [phased array radar](https://bliptext.com/articles/phased-array-radar) system.\nIn addition, signal amplitude is increased across the [microstrip](https://bliptext.com/articles/microstrip) transmission lines by suspending them above the ground plane at a predetermined distance.\nIn other words, they are not in contact with a solid substrate.\nDielectric signal loss is reduced significantly, reducing signal attenuation.\nThis system was designed to boost the performance of the [Monolithic microwave integrated circuit](https://bliptext.com/articles/monolithic-microwave-integrated-circuit) (MMIC), among other benefits.\nA transmission line is created with photolithography.\nA metamaterial lens, consisting of a thin wire array focuses the transmitted or received signals between the line and the emitter / receiver elements.\nThe lens also functions as an input device and consists of a number of periodic unit-cells disposed along the line.\nThe lens consists of multiple lines of the same make up; a plurality of periodic unit-cells.\nThe periodic unit-cells are constructed of a plurality of electrical components; capacitors and inductors as components of multiple [distributed-element circuits](https://bliptext.com/articles/distributed-element-circuit).\nThe metamaterial incorporates a conducting [transmission element](https://bliptext.com/articles/transmission-medium), a substrate comprising at least a first ground plane for grounding the [transmission element](https://bliptext.com/articles/transmission-medium), a plurality of unit-cell circuits composed periodically along the [transmission element](https://bliptext.com/articles/transmission-medium) and at least one [via](https://bliptext.com/articles/via-electronics) for electrically connecting the [transmission element](https://bliptext.com/articles/transmission-medium) to at least the first ground plane.\nIt also includes a means for suspending this transmission element a predetermined distance from the substrate in a way such that the transmission element is located at a second predetermined distance from the ground plane.\n\n## ENG and MNG waveguides and scattering devices\nThis structure was designed for use in waveguiding or scattering of waves.\nIt employs two adjacent layers.\nThe first layer is an epsilon-negative (ENG) material or a mu-negative (MNG) material.\nThe second layer is either a double-positive (DPS) material or a double-negative (DNG) material.\nAlternatively, the second layer can be an ENG material when the first layer is an MNG material or the reverse.\n\n# Reducing interference\nMetamaterials can reduce interference across multiple devices with smaller and simpler shielding.\nWhile conventional absorbers can be three inches thick, metamaterials can be in the millimeter range—2 mm (0.078 in) thick.\n# [A keyless entry system key fob | upload.wikimedia.org/wikipedia/commons/a/a4/SundryKeyFobs2154.jpg]\n\n## General references","revisionCount":0},"hasMore":false,"nextCursor":null}