Electromagnetic Bandgap Surface Research Articles

Metamaterials with angle selective emissivity in the near-infrared

Metamaterials have been previously studied for their ability to tailor the dispersive IR emissivity of a surface. Here, we investigate two metamaterial structures based on an electromagnetic band-gap surface and a dielectric resonator array for use as near-IR emitters with custom angle selectivity. A genetic algorithm is successfully employed to optimize the metamaterial structures to have minimum emissivity in the normal direction and high emissivity at custom off-normal angles specified by the designer. Two symmetry conditions are utilized to achieve emissivity patterns that are azimuthally stable or distinct in the two orthogonal plane cuts.

Metamaterials with custom emissivity polarization in the near-infrared

Metamaterials have been previously studied for their ability to tailor the dispersive infrared (IR) emissivity of a surface. Here, we investigate metamaterial coatings based on an electromagnetic band-gap surface for use as near-IR emitters with custom polarization selectivity. A genetic algorithm is successfully employed to optimize the metamaterial structures to exhibit custom linear, circular, and elliptical polarization. A study is also conducted on a bi-anisotropic slab, showing that anisotropic chirality is required in the metamaterial structure in order to achieve circular or elliptical emissivity polarization.

A Novel Dual-Band Circularly Polarized Antenna Based on Electromagnetic Band-Gap Structure

In this letter, a dual-band polarization-dependent electromagnetic band-gap (PDEBG) surface is designed as a reflector of a dual-band dipole antenna to realize dual-band circular polarization. Experimental and numerical results verify the concept of the low-profile dual-band circularly polarized antenna. The antenna features 10-dB return-loss bandwidths of 13.4% and 3.2% and 3-dB axial-ratio bandwidths of 2.4% and 3.5% in low and high frequency bands, respectively. The proposed antenna can present the same or different circular polarization in two bands based on different designs of the PDEBG.

SECTORAL M-EBG ANTENNA WITH MULTIPOLARIZATION CAPABILITIES FOR WIMAX BASE STATIONS

A novel multipolarized sectoral antenna on a metallic electromagnetic band gap (M-EBG) surface is investigated. The M- EBG structure behaves as a partially re∞ecting surface (PRS) and enhances the directivity of a simple radiating source. The use of metallic structures ofiers a new approach to industrial partners in order to reduce costs and to facilitate design techniques. By using double layers of M-EBG structure working on orthogonal polarizations as a superstrate with a single patch feeding by two ports, multipolarization operation is achieved. This antenna provides vertical, horizontal, 0 - /90 - and circular polarizations with a sectoral radiation pattern in the azimuth plane. M-EBG antennas with sectoral pattern are usually designed only for vertical polarization. In order to verify the results a Bipolar M-EBG Sectoral antenna prototype for WIMAX application (5.15{5.35) GHz is realized and measured. Finally, we study the possibility to generate circular polarization.

Numerical studies of bandwidth of parallel-plate cut-off realised by a bed of nails, corrugations and mushroom-type electromagnetic bandgap for use in gap waveguides

Recently it has been shown that so-called gap waveguides can be generated in the gap between parallel metal plates. The gap waveguides are formed by metal ridges or strips along which local waves propagate, and parallel plate modes are prohibited from propagating by providing one of the surfaces with a texture that generates an artificial magnetic conductor (AMC) or an electromagnetic bandgap (EBG) surface on both sides of the ridges or strips. The bandwidth of the gap waveguide is determined by the cut-off bandwidth of a parallel-plate waveguide where one surface has such a texture (and no ridges or strips). This paper studies the bandwidths (or stop bands) of such parallel-plate cut-offs when the AMC or EBG is realised by a metal pin surface, corrugations or a mushroom surface. It is shown that cut-off bandwidths of up to 4:1 are potentially available, and thereby similar bandwidths should be achievable also for gap waveguides.

Nature-Inspired Optimization of High-Impedance Metasurfaces With Ultrasmall Interwoven Unit Cells

This letter introduces a set of novel designs for high-impedance metasurfaces with ultrasmall interwoven unit cells that achieve increased miniaturization compared to existing literature, yet still provide identical bandwidth performance and excellent field of view. This development makes possible more compact designs for artificial magnetic conducting (AMC) ground planes and electromagnetic band-gap (EBG) surfaces as well as providing the ability to scale these structures to much lower frequencies. In addition, we show that the unit cell geometry can be manipulated via wind-driven optimization (WDO) to precisely control the center frequency of the proposed high-impedance metasurface designs.

Polarisation-dependent electromagnetic bandgap incorporating a slanted sheet via

This study describes a novel sheet via polarisation-dependent electromagnetic bandgap surface. The properties of the surface are shown to vary with the via angle and length selected. The former adjustment causes asymmetric behaviour to linear incident waves and the latter brings about a reduction in inductance and consequent increase in resonant frequency. A 45° inclined via is examined in terms of its response to linear and circularly polarised (CP) waves. It is shown via simulation that linear polarised plane waves can be converted to CP with an axial ratio better than 0.4 dB. The study also demonstrates that at the centre of the design band the surface reflects co-handed waves in response to CP incident waves. Finally, the study details a dual-band CP antenna with a single port, achieved by exciting the surface with a bazooka-balun dipole.

Wideband Miniaturized Polarization-Dependent HIS Incorporating Metamaterials

The use of metamaterial as a substrate for a high-impedance surface (HIS), which can miniaturize the size and significantly enhance the axial ratio bandwidth of a polarization dependent HIS, is introduced. The electromagnetically small Ω-type inclusions have been used to achieve the effective permeability and permittivity greater than that of the host dielectric. It is demonstrated that the proposed high-impedance surface can provide performance superior to the polarization-dependent electromagnetic band-gap (PDEBG) surfaces. This complex artificial ground plane is designed utilizing two reversed Ω patterns back to back on each side of a substrate board to avoid chiral effects.

Microstrip Patch Antennas on Tunable Electromagnetic Band-Gap Substrates

A tunable metamaterial in integrated circuit structures is investigated through an example of a microstrip patch antenna on a mushroom-type electromagnetic band-gap (EBG) structure. The patch antenna is designed as a half-wavelength resonator of an EBG loaded microstrip transmission line. The operating frequency of a patch antenna can be switched and controlled dynamically by loading diode switches in between vias and the ground plane. When the switches are on, the EBG surface is short to the ground and is at its on-state; while when the switches are turned off, the EBG surface is dc open and is at its off-state. It is found that the resulting patch antenna in-band resonant frequencies are very different at these two states. Antenna dual-band frequencies, gain, efficiency, and radiation patterns are characterized. The designed switchable EBG-patch antenna is fabricated and tested in these two states. The measurement is found in good agreement with simulation. An example is also given for the case of selected switches within the EBG elements to tune dynamically the resonant frequency.

Reduction of Patch Antenna Coupling by Using a Compact EBG Formed by Shorted Strips With Interlocked Branch-Stubs

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter presents a new type of planar electromagnetic band-gap (EBG) surface composed of short-circuited microstrips densely coupled with each other through interlocked branch stubs. With respect to a conventional mushroom surface, this structure exhibits a better space-wave decoupling performance due to the soft nature of the surface. With respect to other soft surfaces, like shorted strip already introduced in the literature, the present solution possesses better miniaturization properties, thus allowing the use of lower permittivity and consequent improvements when integrated in planar dense arrays. The experimental results demonstrate a decoupling until 38 dB in both planes for patches separated by only one half free-space wavelength. </para>

Comparison of bandwidths of mushroom-type electromagnetic bandgap surfaces and corrugated and strip-type soft surfaces when used as narrow ground planes

The authors compare different types of corrugated and strip-loaded soft surfaces and mushroom-type electromagnetic bandgap (EBG) surfaces in terms of the bandwidth of a system-related performance parameter, when they are used as narrow ground planes to reduce back radiation. To this aim an incremental electrical source on an infinitely long ground plane of finite width is analysed. The strip-loaded soft surfaces are improved with periodic via holes (like in mushroom-type EBGs) behaving as conducting walls and making the strips appear as tilted horizontal corrugations. The via period as well as their locations either in the centre or at the edge of each strip are investigated. This is also done for mushroom-type EBGs. The results show that the surfaces with the largest bandgap do not necessarily have the largest bandwidth. Still, the size of the bandgap seems to be an upper limit for the bandwidth. The results show that corrugations have better performance (in terms of bandwidth and lower level of back radiation) than both strip-loaded and mushroom-type EBG surfaces, and that wide ground planes behave better than narrow ones. In addition, strips with vias are seen to have similar performance as mushrooms with via holes for TM case with respect to the surface normal, that is, transverse polarisation relative to length axis of ground plane, whereas the strip version has larger bandwidth than the mushrooms for TE case, that is longitudinal polarisation.

Dual band tunable EBG

An electromagnetic bandgap (EBG) surface that can be independently tuned over two separate frequency bands is demonstrated. The EBG consists of a dual layer of square element based designs with varactor diodes. The EBG tuning ranges for each band were from 600 to 1200 and 1700 to 2600 MHz.

Design of Three-layer Circular Mushroom-like EBG Structures

In this paper two types of three-layer mushroom-like electromagnetic band-gap (EBG) surfaces with circular patches are investigated. One of them consists of a square array of circular patches and the other one consists of a triangular array of circular patches in upper and lower layers. Guidelines for designing a ground plane for low proflle antenna applications are presented using the re∞ection phase characteristics. The efiect of some parameters of the three-layer structures on the re∞ection phase characteristic is studied. The frequency band in which a wire antenna adjacent to the three-layer EBG surface has good matching is determined by investigating the re∞ection phase characteristics of the EBG ground plane.

A Double-Surface Electromagnetic Bandgap Structure With One Surface Embedded in Power Plane for Ultra-Wideband SSN Suppression

In this letter, a double-surface electromagnetic bandgap (EBG) structure with one EBG surface embedded in power plane is proposed for ultra-wideband simultaneous switching noise (SSN) suppression in printed circuit boards. The SSN suppression bandwidth is broadened to wider than 30 GHz with a low start frequency by combining traditional EBG structure and the coplanar EBG structure which is embedded in the power plane. Because the coplanar EBG surface is embedded in the power plane, no additional metal layer is introduced by the double-surface EBG structure. Simulations and measurements are performed to verify the broadband SSN suppression, high performance is observed.

Radiation Characteristics of a Microstrip Patch Over an Electromagnetic Bandgap Surface

Radiation characteristics of a microstrip patch over an electromagnetic bandgap (EBG) substrate are investigated in this paper. This paper focuses on a mushroom-type EBG structure, although the design is applicable to various EBG profiles. The patch antenna is modeled as a half-wavelength resonator of an EBG-loaded microstrip transmission line. Through a full-wave eigenmode analysis of a microstrip line on an EBG structure, it is found that the resonant patch will not see a high-impedance surface (HIS), but rather it is coupled to the EBG structure as an open cavity resonator. Due to strong near-field coupling, the propagation characteristics including the bandgap zones are very different with or without the patch cover. The use of an EBG structure as a bulk material for antennas is seen inappropriate. The EBG surface is found to have the effect of reducing the patch resonant length and bandwidth. A prototype of a microstrip line proximity fed to a patch antenna is fabricated and tested to verify the analysis.

Some novel design for RFID antennas and their performance enhancement with metamaterials

AbstractIn this paper we discuss a number of UHF/RFID tag designs including the hybrid loop (Chen and Hsu, International Symposium on Antennas and Propagation, Korea, Vol. 3, 2005, 1045–1048), dual crossed‐dipoles, the dual crossed‐dipoles utilizing an inductively coupled feed (Choo and Ling, Electron Lett 39 (2003) 3080–3081). We have carried out extensive parametric studies in the process of analyzing the characteristics of the earlier‐mentioned antennas, and have investigated several techniques (Choo and Ling, Electron Lett 39 (2003) 3080–3081), including meandering, for size‐reduction of these antennas. A design methodology based on the Genetic Algorithm (GA) is presented for the optimization of conformal antennas with Electromagnetic Bandgap (EBG) surfaces (Mittra, Proceedings of International Symposium on Antennas and Propagation 2005 (ISAP2005) Seoul, Korea, 2005, 325–328; Sievenpiper et al., IEEE Trans Microwave Theory Tech 47 (1999), 2059–2074) to improve the antenna performance. The EBG characteristic is realized by utilizing a Frequency Selective Surface (FSS) placed above a thin dielectric substrate backed by a metallic ground plane to act as an Artificial Magnetic Conductor (AMC). The antenna is then placed above the EBG surface to create a conformal integrated EBG ‐ antenna. The initial design of the AMC is carried out by synthesizing a surface whose reflectivity is “+1”, for a normally incident plane wave. However, since the antenna situated above it produces not just a single plane wave but a spectrum of these waves, it becomes necessary to refine the initial design to optimize the performance of the antenna/AMC composite, and techniques for doing this are discussed in the paper. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 858–867, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22265

Enhanced Bandwidth Artificial Magnetic Ground Plane for Low-Profile Antennas

In this letter, it is shown that using magneto-dielectric materials as substrate can increase the in-phase reflection bandwidth of electromagnetic bandgap (EBG) structures. To show this, a compact wideband EBG structure is designed and simulated. The numerical results show that this EBG has an in-phase reflection bandwidth of 70% which is several times greater than a conventional EBG resonating at the same frequency. Additionally, the new EBG surface has a smaller cell size, an important feature in the design of small antennas. As a demonstration of the effectiveness of the new structure, a low-profile unidirectional spiral antenna is designed to operate from 8 to 18 GHz. The improvement in the voltage standing wave ratio (VSWR) and gain of this antenna is presented while comparison is made to the case when using conventional EBG surface.

Investigation of EBG surface performance for high-precision GPS applications

A mushroom-like electromagnetic bandgap (EBG) surface for interference mitigation in GPS L2 and L1 band is presented. This printed metallo-dielectric structure is designed to act like commercially available choke rings (cylindrically corrugated surface). Measurements exhibit comparable performance, while weight and thickness are significantly reduced.

Comparison of bandgaps of mushroom-type EBG surface and corrugated and strip-type soft surfaces

Corrugated and strip-loaded soft surfaces are characterised in the same way the electromagnetic bandgap (EBG) surfaces are characterized, that is, in terms of the bandgaps in their dispersion diagrams. The strip-loaded surfaces are provided with metalised via holes, and both central and lateral locations of these are investigated. It is found that strip-loaded surfaces with vias have the same bandgaps as mushroom-type EBG surfaces of the same period. It is also found that the strip-loaded surface can be designed to have the bandgap appearing at lower frequency than the mushroom surface, by locating the vias at the edge rather than in the middle and by optimising the period of the vias along the strips.

Full-wave analysis of bound and leaky modes propagating along 2D periodic printed structures with arbitrary metallisation in the unit cell

A full-wave numerical approach for the analysis and design of two-dimensional printed periodic structures on a grounded dielectric slab is presented. Electromagnetic band-gap surfaces, metamaterials and leaky-wave antennas are important special cases of structures that can be analysed. The proposed technique permits the analysis of an arbitrary metallisation within the unit cell; it is based on a mixed-potential integral equation solved by the method of moments in the spatial domain. Two-dimensional periodic vector and scalar Green&apos;s functions are derived in the spectral domain and an appropriate choice of the spectral determination for each spatial harmonic is performed to properly account for leakage effects. The proposed approach is used to calculate the real propagation wavenumber for surface waves in their pass-band regimes, propagating at arbitrary angles on two-dimensional periodic printed structures. Complex propagation wavenumbers can be derived as well for both bound modes in their stop-band regimes and proper and improper leaky modes in their relevant physical and non-physical regions. Results for a reference uniplanar compact photonic bandgap structure are reported demonstrating how the application of this rigorous technique provides a new detailed picture of the different modal behaviours and a more accurate determination of its band-gap zones.