High Impedance Surface Research Articles

A novel Dual-Band Double-Sided High-Impedance Surface (DB-DS-HIS) with systematic design methodology

This paper presents a systematic design methodology of dual-band double-sided high-impedance surface (DB-DS-HIS). The high impedance characteristics seen from both sides of the structure at two distinct frequencies are investigated theoretically based on the transmission line (TL) model and the surface impedance method. The proposed DB-DS-HIS is presented and parametric study on the reflection properties of the double-sided HIS structure loaded with additional patches/rings is given. Finally, the proposed DB-DS-HIS unit cells are combined as a chessboard structure to reduce the radar cross section (RCS). More than 15 dB RCS reduction in the first frequency band from 8 GHz to 12 GHz with maximum reduction of 37 dB at 10 GHz and more than 10 dB RCS reduction in the second frequency band from 14 GHz to 16 GHz with maximum reduction of 29 dB at 14.7 GHz is achieved. Since the structure is double sided, the RCS of the chessboard structure is reduced at the two frequency bands from both sides.

Corporate Feed, Compact 2X2 Array Antenna With Enhanced Radiation Characteristics using Metamaterial Structure

In current study, mushroom type metamaterial substrate is designed to operate at ISM band and is embedded in 2X2 array as a ground. Unique properties of mushroom type metamaterial substrate like as high impedance surface (HIS) helped in design of low aperture antenna, Artificial magnetic conductor (AMC) helps in enhancing the radiation characteristics and Forbidden band gap (FBG) helps in suppressing transverse electric (TE) and transverse magnetic (TM) wave propagation hence point of mutual coupling and side lobe levels are reduced. So, 2X2 array antenna with corporate feed resonating at 2.5GHz is embedded by array of mushroom type metamaterial unit cells is designed in HFSS and obtained results are compared with 2X2 array resonating at 2.5GHz on conventional conducting ground results. An enhancement in impedance band width of 2.47%, gain of 2.91dB and with lowered side lobe reduction of 3.74dB.

Orientation-Insensitive and Normalization-Free Reading Chipless RFID System Based on Circular Polarization Interrogation

A novel normalization-free reading scheme to recover data encoded in chipless radio frequency identification (RFID) tags is presented. The proposed approach exploits the circular polarization to isolate the field scattered by the tag from that of surrounding objects. The desired polarization mismatch is achieved by exploiting the properties of high-impedance surfaces that can suitably manipulate the reflected field. A thorough analysis of the interaction between the circularly polarized (CP) interrogation and the field scattered by the chipless RFID tag as well as the hosting platform is provided. The proposed method does not require any a priori calibration if a reading antenna with a suitable axial ratio is available. More importantly, the CP-based reading approach guarantees the correct tag detection regardless of the tag orientation. The case of the tag mounted on metallic platform is also analyzed and it is demonstrated that the circular polarization reading procedure is robust under the hypothesis of a proper axial ratio of the probing antennas. The minimum requirements of axial ratio are derived by using a theoretical model. Measurements confirmed the speculations obtained through the theoretical analysis both in the case of low-scattering items as well as for metallic platforms.

Phase-Induced Frequency Conversion and Doppler Effect With Time-Modulated Metasurfaces

Metasurfaces consisting of electrically thin and densely packed planar arrays of subwavelength elements enable an unprecedented control of the impinging electromagnetic fields. Spatially modulated metasurfaces can efficiently tailor the spatial distribution of these fields with great flexibility. Similarly, time modulated metasurfaces can be successfully used to manipulate the frequency content and time variations of the impinging field. In this paper, we present time-modulated reflective metasurfaces that cause a frequency shift to the impinging radiation, thus realizing an artificial Doppler effect in a non-moving electrically thin structure. Starting from the theoretical analysis, we analytically derive the required time modulation of the surface admittance to achieve this effect, and present a realistic time-varying structure, based on a properly designed and dynamically tuned high-impedance surface. It is analytically and numerically demonstrated that the field emerging from the metasurface is up-,down-converted in frequency according to the modulation profile of the metasurface. The proposed metasurface concept, enabling a frequency modulation of the electromagnetic field on-the-fly, may find application in telecommunication, radar, and sensing scenarios.

3d Beam Reconfigurable THz Antenna with Graphene-Based High-Impedance Surface

In this letter, a novel 3D multi-beam reconfigurable THz loop antenna capable of steering its main beam in the semi-sphere space (θ ϵ {0°, ±5°, ±10°}; φ ϵ {0°, 30°, 60°, 90°, 120°, 150°}) is presented. The antenna is based on a switchable circular high impedance surface (HIS) using the graphene–metal hybrid approach. The effect of gate voltage on the conductivity of graphene and the switchable reflection characteristic of the graphene-based HIS are combined in the design. Changing the chemical potential of different graphene-based HIS units can effectively adjust the beam direction. The performance of the antenna is analyzed through its reflection coefficients and gain radiation patterns, and simulated results show that the maximum gain can reach 3.23 dBi at 0.5 THz.

Miniaturized-Element Frequency Selective Surface Metamaterials: A Solution to Enhance Radiation of RFICs

In this article, a technique to improve the radiation characteristics of an active CMOS circuit is presented. A miniaturized-element frequency selective surface (MEFSS) cover is utilized on top of the chip to provide gain enhancement, which is essential for many applications such as radar and communication systems. This is important due to the restrictions on the thickness of metallic layers, losses in substrate, and limitations in real estate. The MEFSS cover consists of partially reflecting surface (PRS) and high-impedance surface (HIS) creating a Fabry–Perot-type cavity (FPC). When the MEFSS structure is used, the height of FPC can be reduced without causing any deterioration to the antenna radiation. A proximity patch antenna is embedded in the HIS layer, which is fed by a small metallic trace on the last layer of chip using the coupling mechanism. By utilizing the transverse-equivalent network (TEN) of the structure and imposing the resonance condition, the geometrical parameters of the MEFSS unit cell is calculated. For demonstration purposes, a scaled MEFSS cover for gain enhancement at the center frequency of 10 GHz is designed, fabricated, and tested. The measured results, which are in agreement with simulations, show that the proposed technique is reliable in practice and gain enhancement of 9 dB can be achieved for a single-patch antenna.

Dual band circular polarized bow tie slotted patch antenna over high impedance surface for WiMAX application

AbstractA novel planar dual-band bow-tie slotted patch antenna backed by high-impedance surface (HIS) is designed at 2.5 and 3.5 GHz for wireless application. The antenna employs coplanar waveguide fed patch and bow-tie slot as radiating elements. The bow-tie slot enables dual-band operation for the antenna. The HIS is made asymmetric in design to make it polarization dependent. This polarization-dependent HIS is eventually designed to reflect circularly polarized waves from linearly polarized incident waves.

A low profile tunable microwave absorber based on graphene sandwich structure and high impedance surface

In this paper, a low profile dynamically tunable microwave absorber is proposed, which consists of high impedance surface (HIS) and graphene sandwich structure (GSS). We theoretically demonstrate and experimentally verify that the proposed absorber can provide a dynamically tunable reflection range from larger than -3dB to less than -30 dB (corresponding to the absorption range from 50% to 99.9%) at opera-ting frequency of 11.2GHz by external bias voltage. The entire thickness of this absorber is only 2.8mm, nearly one tenth of working wavelength. In addition, a modified equivalent circuit model is proposed to explicate its absorption mechanism. At last, we fabricate a prototype absorber, and measure its absorption in anechoic chamber. The experimental results agree well with the full wave simulation results. This work may provide a reference for design and fabrication of dynamically tunable microwave absorber based on large-scale graphene and may promote the actual applications of graphene at microwave frequency.

Broadband Low-RCS Phased Array With Wide-Angle Scanning Performance Based on the Switchable Stacked Artificial Structure

A novel and simple switchable stacked artificial structure (SAS) is proposed and studied in phased arrays to realize a smart integration of broadband radar cross section (RCS) reduction and scanning range expansion. The proposed SAS is composed of a frequency selective surface (FSS) and a metamaterial absorber (MA). The lower part of the SAS can be switched between an FSS and a surface-waveguide (SWG) high-impedance surface (HIS) hybrid structure which can be used for wide-beam antenna design and array mutual coupling reduction. The upper part of the SAS can be seen as an MA. A linear phased array is presented and investigated based on the proposed switchable SAS. When the phased array is switched to its working mode, the SWG-HIS hybrid structure plays an important role to support a wide-angle scan from −75° to +75° with low sidelobes. When the phased array is shut down, the FSS-MA stacked structure can realize a low-RCS design in the frequency range of 0–11.2 GHz. An array prototype which operates at 4.6 GHz is fabricated and measured. The measured results have validated the radiation and scattering performance of the designed phased array.

Wideband and high gain tuning fork shaped monopole antenna using high impedance surface

This paper formulates a design methodology for a low profile monopole antenna backed by a high impedance surface (HIS). The formulated design achieves high gain and high directivity while maintaining the low-profile nature. It is demonstrated that the choice of the monopole antenna does not hamper the enhancement of gain due to HIS backing. The designed HIS is a uniplanar structure designed to have the advantage of suppressing surface waves while image current and antenna current are in phase with each other at each frequency. The fabricated design exhibits a wide bandwidth ranging between 2.68 GHz and 3.65 GHz with a relative impedance bandwidth of 32.3% and a gain increase of 4.5 dBi as compared to the unbacked antenna. A comprehensive simulation study has been carried out which helps in verification of the proposed methodology for strategizing the fabrication process.

Demonstration of a self-polarizing dual-band single-feed circularly polarized Fabry-Perot cavity antenna with a broadband axial ratio

A cost-efficient low profile dual-band circularly polarized (CP) fabry-perot cavity antenna (FPCA) with large axial ratio (AR) bandwidth is experimentally demonstrated in this paper. The utilized partially reflective surface (PRS) which comprises an array of square loops in one side and asymmetric meander-lines in another side of dielectric layer, is designed so as to realize a roughly linear phase of transmittance in a wide frequency band for both LP components with nearly 90° phase difference between them. A single-layer high impedance surface (HIS) is employed to compensate the phase difference between the two LP components of the reflected waves from the PRS. The cavity is excited by a linearly polarized (LP) primary source with embedded two parasitic patches, which are all aligned along an optimal slant angle equal to 55° to not only generate two notches within the band 14–15.5 GHz, but also compensate the difference between magnitudes of two orthogonal components of transmitted waves through the PRS. A prototype with the dimensions of 1.7λmin×1.7λmin×.41λmin is fabricated and the measurement results show that the peak gain of antenna is 10 dBi and 9.2 dBi at 14.125 GHz and 15.375 GHz, respectively and the AR is below 3 dB from 13.5 GHz to 15.7 GHz (15%).

An Axial Compression Planar Lens Antenna Based on Discrete Transformation Electromagnetics Using High-Impedance Surface Cells

A two-dimensional (2-D) convex lens is reshaped and compressed into a 2-D flat lens with a compression ratio of 52.6% by discrete transformation electromagnetics. The single-layer high-impedance surface cells are used to fill with the compressed zone to form a planar flat lens. A parallel-plate waveguide and a 1/4 λ reflector are used to ensure that the electromagnetic energy generated by the monopole flows to the lens. The planar lens antenna, 4.35 λ × 4 λ on the lens plane and 0.375 λ tall, is fabricated and measured in TM mode at 7.5 GHz. The measured data indicate that the proposed planar lens antenna achieves an 11.3 dBi gain, 16.7° half-power beamwidth on H -plane, and almost 260 MHz impedance bandwidth for S 11. The joint design of discrete transform electromagnetics and high-impedance surface cells is a new method, which has strong reference value for the miniaturization of other lens antennas.

Passive Matched Mushroom Structure for a High Sensitivity Low Profile Antenna-Based Material Detection System

A passive multi-layered structure based on a mushroom high-impedance surface is proposed as a part of a high sensitivity low profile antenna-based material detection system. The system consists of an interrogating antenna placed outside the near field of a three-layered planar sensor. The sensor is a periodic structure containing $10\times 10$ unit cells with overall dimensions of $180\,\,\text {mm}\times 180\,\,\text {mm}\times 10.2\,\,\text {mm}$ . Achieving high sensitivity at a large monitoring distance (150 MHz per unit relative permittivity at 430 mm), this sensor provides sensing capability in hazardous or inaccessible environments while also maintaining independence of the sensor and the antenna for greater system flexibility. Material detection is based on wireless tracking of frequency shifts in the absorption peak of the sensor. These shifts arise from changes in the permittivity of a sensing layer sandwiched between a bottom resonant layer (a mushroom high-impedance surface) and a top inductive matching layer. Two independent mechanisms contribute to the resonant shifts for heightened sensitivity at a low profile. Two sets of experiments were performed to verify the operation of the sensor over a wide range of solid and liquid material permittivities. First, solid samples of Teflon, Plexiglass, and Rogers microwave laminates (TMM06 and TMM10) were detected with frequency shifts up to 1233 MHz. Second, liquid samples of isopropyl alcohol, ethanol, methanol, and de-ionized water were detected with corresponding frequency shifts up to 130 MHz. Measurements are performed using a single reader antenna to reduce the cost and complexity for in-field applications.

Graphene‐based low side‐lobe microwave horn antenna

In this study, a novel method is proposed to control and reduce the side-lobe level (SLL) of the pyramidal horn antennas. In this method, graphene sheets are deposited on the antenna walls to taper the aperture field leading to pattern engineering with the goal of the SLL reduction. In essence, graphene sheet acts as a high-impedance surface and hinders electromagnetic power from reaching to the horn antenna aperture edges, in such a way that the diffraction phenomenon could be drastically diminished. The proposed design is numerically analysed and optimised using full-wave three-dimensional simulation methods. Numerical full-wave results illustrate more than 17.6 dB reduction in the SLL of the proposed antenna.

Circularly Polarized Fabry–Perot Antenna Using a Hybrid Leaky-Wave Mode

This paper presents the spectral Green’s function (GF) to analyze Fabry–Perot antennas to generate circular polarization (CP). The structure consists of a single cavity created between a partially reflective surface and a high impedance surface, fed by a low directive, linearly polarized source. Elements in the antenna are characterized by tensor impedances. It allows conceiving a circularly polarized antenna supporting a single hybrid leaky-wave mode. Residue analysis is used to demonstrate that a single hybrid leaky-wave mode is sufficient to generate CP. The tool is validated by an antenna design matched over a relative bandwidth of 28.5% with an axial ratio lower than 3 dB.

Multilayer dielectric substrate for improved Raman spectroscopy

To enhance Raman scattering, we propose a multi-layer substrate which behaves similar to a magnetic mirror or what is also known as high-impedance surface (HIS). Due to this property, the electric field of the illuminating light is increased by a factor of two. This field enhancement doubles the amplitude of the Raman signal generated by the molecules residing on this multi-layer structure. On the other hand, the introduced multi-layer structure is designed to operate as a filter for the scattered field at the Rayleigh wavelength, so that the wave transmitted through this structure mainly contains the Raman signal with 45 dB rejection of the Rayleigh wavelength. The designed substrate reduces the complexity of the conventional Raman setup and helps to realize a more compact setup.

An Approximate Multiconductor Transmission Line Model for an Antenna Loaded by High-Impedance Unit Cells

We present a transmission line model for a microstrip line or antenna above a row of high-impedance unit cells, such as those used in a high-impedance surface (HIS) ground plane. The model is built on a multiconductor transmission line circuit description of the joint microstrip and HIS cell structure as stacked microstrip lines. Discontinuities in the HIS cell layer are modeled as circuit elements using well-known closed-form expressions. S-parameters predicted by the transmission line model agree with full-wave simulations from low frequencies to above the parallel resonance of the HIS unit cells. The model also provides an approximate forward prediction of the impedance behavior of antennas above HIS ground planes, which cannot be obtained using the reflection phase method.

Energy Selective Surface With Power-Dependent Transmission Coefficient for High-Power Microwave Protection in Waveguide

This paper presents an energy selective surface (ESS) for high-power microwave (HPM) protection in waveguide, which has a nonlinear transmission response and can adaptively react to the power intensity of an incident wave. A prototype of four unit cells loaded with p-i-n diodes is designed and fabricated in L -band. The nonlinear and adaptive transmission characteristics are demonstrated by the waveguide measurements both in the time domain and frequency domain. On condition of signal power below 35 dBm, the wave in the interested band can propagate through waveguide with a low insertion loss down to 1 dB; while on condition of signal power above 47 dBm, high power would render the ESS into a high-impedance surface, and the incident wave would be reflected and dissipated with a transmission coefficient of less than -10 dB, thereby providing the HPM protection ability. Furthermore, the subsequent simulations illustrate that the inserted ESS will not worsen the radiation patterns of the following horn antenna and the induced high-order modes in waveguide keep negligible values below -65 dB.

A Miniaturized Broadband High-Impedance Surface With Flexible Circular Polarization Sense

This communication presents a miniaturized ( $0.084\lambda _{0} \times 0.044\lambda _{0}$ ) dual-layered broadband polarization-dependent high-impedance surface (PDHIS). The unit-cell (UC) structure consists of periodic narrow horizontal patch arrays and vertical meander lines on the top and bottom layers of a thin substrate ( $0.012\lambda _{0}$ ), respectively. Using this arrangement, the phase difference between the orthogonal polarization’s of the reflector is enhanced to 180° ± 30° over a wide range of frequencies. The UC of the proposed PDHIS is 88.7% smaller and the measured 3-dB axial-ratio bandwidth is 168.27% broader than a conventional anisotropic HIS. Also, the proposed PDHIS is polarization agile and the circular polarization sense can be easily controlled by changing the alignment of the reflector with respect to the incident plane wave. An equivalent circuit model of the dual-layered anisotropic HIS is presented and the proposed structure is validated using simulations and measurements.

UHF Reader Antenna System for Near and Far-Field RFID Operation

In order to detect the RFID tags kept inside an enclosure, the reader antenna can couple energy into another antenna kept in the near-field region. To detect the tags placed in the far-field, the reader antenna should have a good gain. Usually, these two requirements compete with each other due to the effect of coupling on the frequency of operation of the antenna system. In this paper, modification to a loop antenna is proposed such that it can operate in both near and far-field. Loop antenna with high impedance surface reflector results in a low-profile antenna pair where both the antennas can interchangeably operate in near-field and far-field, with their operating frequency band independent of the spacing between the antennas. The performance of the proposed antennas is compared with that of several other antennas by measuring the read range of RFID tags. It is found that the proposed antennas perform better in comparison with the other antennas when detecting the tags placed inside an enclosure. When operating as a far-field antenna, their performance is very close to that of a conventional RFID reader antenna which is optimized only for far-field operation.