Artificial Magnetic Conductor Surface Research Articles

Contactless Air-Filled Substrate Integrated Waveguide

The contactless version of the air-filled substrate integrated waveguide (AF-SIW) is introduced for the first time. The conventional AF-SIW configuration requires a pure and flawless connection of the covering layers to the intermediate substrate. To operate efficiently at high frequencies, this requires a costly fabrication process. In the proposed configuration, the boundary condition on both sides around the AF guiding medium is modified to obtain artificial magnetic conductor (AMC) boundary conditions. The AMC surfaces on both sides of the waveguide substrate are realized by a single-periodic structure with the new type of unit cells. The PEC–AMC parallel plates prevent the leakage of the AF guiding region. The proposed contactless AF-SIW shows low-loss performance in comparison with the conventional AF-SIW at millimeter-wave frequencies when the layers of both waveguides are connected poorly.

Design of a randomised arrangement AMC surfaces for RCS reduction based on equivalent circuit modelling

This study aims to present a thin and broadband meta-surface for both mono-static and bi-static radar cross-section (RCS) reduction being able to operate in large range of incident angles and different polarisations. Meta-surfaces are formed through the combination of two artificial magnetic conductor (AMC) cells arranged in periodic and randomised fashions in order to suppress the scattered fields in low levels in all directions as well as minimising the maximum RCS of the metallic surface. By appropriate design of each AMC, and using equivalent circuit method, the reflection coefficients of these surfaces are designed in a way to reach 180 (±37°) phase difference over a wide range of frequencies and incident angles. The bandwidth for 10 dB mono-static RCS reduction is about 53% for both periodic and randomised structures at the normal incidence. It is illustrated that the randomised arrangement structure has 3 dB lower maximum bi-static RCS compared with the periodic structure. Finally, the periodic and randomised arrangement prototypes are fabricated and measurements of their mono-static RCS are conducted. The validity of the study design is fulfilled by achieving an acceptable agreement between the measured and simulated results.

Low-Profile Conical-Pattern Slot Antenna With Wideband Performance Using Artificial Magnetic Conductors

A slot antenna with conical patterns and wideband performance based on artificial magnetic conductors (AMCs) is presented in this paper. It has four symmetrical square radiating slots and a meandered feeding network etched on the both sides of the upper substrate to achieve a compact size. Wideband performance is achieved by tuning the resonant frequencies of the one-wavelength slot and quarter-wavelength monopole modes close to each other. The electric fields generated by these four slots cancel each other, resulting in a radiation null in the center. And the AMC surface converts the radiation pattern into conical pattern. The simulation and measurement results on $S_{11}$ , radiation patterns, efficiencies, realized gains, and SAR values are given. The performance of the proposed antenna in a practical helmet model is studied. The results show that the proposed antenna has an impedance bandwidth of 4.83–6.25 GHz (1.42 GHz, 25.6%), maximum gain of 6 dBi at the elevation angle of 36°, and low 1 g SAR values of less than 0.22 W/kg for the application of the IEEE 802.11a WLAN system.

Wideband low‐profile CPW‐fed slot‐loop antenna using an artificial magnetic conductor

A wideband low-profile slot-loop antenna is proposed based on an artificial magnetic conductor (AMC) reflector which is applied to a slot-loop antenna to obtain directional radiation patterns. Compared with an antenna using a metal reflector, the AMC reflector can reduce the profile of the antenna and enhance operating bandwidth. The AMC consists of 4 × 6 patches with ring slots and slits. A coplanar waveguide is introduced to the proposed slot-loop antenna so that the antenna can directly attach to the AMC surface. Thus, a low profile of 0.05λL is realised (λ L is the wavelength at the lowest operating frequency). Simulation and experimental results indicate that the proposed antenna obtained a 37.9% impedance bandwidth, a 36.7% 3-dB gain bandwidth, and a 6.85 dBi peak gain.

A Low-Profile Dual-Polarized Dipole Antenna Using Wideband AMC Reflector

A low-profile dual-polarized dipole antenna using wideband artificial magnetic conductor (AMC) reflector with stable radiation pattern for use in 2G/3G/4G base stations operating from 1.7 to 2.7 GHz is presented. The antenna consists of a pair of crossed-dipoles and a wideband AMC reflector which consists of an AMC surface, a metallic ground plane, and the air substrate between them. The AMC is designed to operate with 90° reflection-phase bandwidth of 1.64–2.88 GHz (54.8%). Compared with using perfect electric conductor reflector, the profile height of the dual-polarized dipole antenna using AMC reflector is reduced by half from 36 to 18 mm, resulting in the lowest-profile 2G/3G/4G base station antenna. Six metallic ground walls are used to stabilize the radiation pattern, and the resulted half-power beamwidths are around 68±3° and 81±3° in the H- and V-planes, respectively, across the operating band. More measured results show that wide impedance bandwidths of 1.67–2.98 and 1.64–3.05 GHz for the two input ports, isolation of more than 25 dB, and cross-polarization of less than −20 dB are achieved.

A Wideband Beam-Steerable Slot Antenna Using Artificial Magnetic Conductors With Simple Structure

A beam-steerable slot antenna with simple structure and wideband performance using artificial magnetic conductors (AMC) is presented in this paper. It has a simple structure, and consists of one cross-shaped main radiating slot, two parasitic slots with two p-i-n diodes as the reflectors, and an AMC surface. The main radiating slot has an electrical length of about 1- $\lambda $ to achieve a wideband performance. By turning on/off the p-i-n diodes on these two parasitic slots, the main lobe of the radiation pattern can be steered. The AMC surface is used to make the antenna radiate directionally reducing the back lobe simultaneously. A design procedure of tuning the proposed antenna to other frequency band is also given. The simulation and measurement results, including $S_{11}$ , radiation patterns, and realized gains are illustrated. Results show that the main lobe direction of the radiation pattern of the proposed antenna can be tuned among 0°, −36°, and 36° with the peak gains of more than 7 dBi in the operating bandwidth from 4.9 to 5.5 GHz.

Radar Cross Section Reduction of Low Profile Fabry-Perot Resonator Antenna Using Checker Board Artificial Magnetic Conductor

This paper presents a novel low profile, high gain Fabry-Perot resonator antenna with reduced radar cross section (RCS). An artificial magnetic conductor which provides zero degree reflection phase at resonant frequency is used as the ground plane of the antenna to obtain the low profile behavior. A checker board structure consisting of two artificial magnetic conductor (AMC) surfaces with antiphase reflection property is used as the superstrate to reduce the RCS. The bottom surface of superstrate is perforated to act as partially reflective surface to enhance the directivity of antenna. The antenna has a 3 dB gain bandwidth from 9.32 GHz to 9.77 GHz with a peak gain of 12.95 dBi at 9.6 GHz. The cavity antenna also has reduced reflectivity with a maximum reduction of 14.5 dB at 9.63 GHz.

Chessboard AMC Surface Based on Quasi-Fractal Structure for Wideband RCS Reduction

A chessboard artificial magnetic conductor surface based on the quasi-fractal structure is proposed for wideband radar cross-section (RCS) reduction. The chessboard configuration is formed by two different cells with 180° ± 37° phase difference over more than 90% frequency bandwidth. The quasi-fractal structure is utilized to achieve the wideband and compact characteristics. Monostatic and bistatic RCS of the proposed chessboard surface are analyzed, and the results are compared with those of equal-sized perfect electric conductor ground plane. Because the scattered fields of the chessboard surface are redirected toward four quadrants, a remarkable RCS reduction of 10 dB can be realized from 5.4 to 14.2 GHz. Measured results of the fabricated prototype satisfactorily agree with the simulated ones.

Broadband Dual-Polarized Dual-Dipole Planar Antennas: Analysis, Design, and Application for Base Stations

In this article, we propose a compact ±45° dual-polarized dual-dipole (DPDD) antenna for second-, third-, and fourth-generation (2G/3G/4G) long-term evolution (LTE) base stations. The antenna consists of two perpendicularly crossed dual-dipole elements. Each dual-dipole element is directly fed by a coaxial cable. Two dual-dipole elements are printed on the same substrate, making the antenna planar and compact. Due to the coupling between two crossed dual-dipole elements, the antenna can achieve a broad bandwidth of 51% for a return loss greater than 15 dB (1.61-2.71 GHz) with a high isolation of 30 dB. The dual-polarized antenna has a gain of 9 dBi and a halfpower beamwidth (HPBW) of 65 ± 5° for ±45° polarization with a flat metallic reflector. For applications in LTE700/GSM850/900 base stations, a new artificial magnetic conductor (AMC) surface is introduced to replace the metallic reflector. It is shown that the antenna height can be significantly lowered from 105 mm (0.29λ0.83, where λ0.83 is the freespace wavelength at the frequency of 0.83 GHz) for a metallic reflector to 31.52 mm (0.087λ0.83) for an AMC surface while a broad bandwidth of 52% (0.68-1.16 GHz) is still achieved. The broadband ±45° antenna is described in the Broadband ±45° section, and the ±45° antenna with an AMC surface is demonstrated in the DPDD Antenna with an AMC Surface section.

Artificial magnetic conductor-based circularly polarized crossed-dipole antennas: 1. AMC structure with grounding pins

In this paper, we analyze low-profile circularly polarized (CP) antennas comprising a crossed-dipole radiator on finite artificial magnetic conductor (AMC) surfaces. The crossed dipole is fed by a pair of vacant-quarter printed rings to produce CP radiation. The AMC structure consists of a lattice of square metal plates on a grounded dielectric substrate with connecting pins between the patches and the ground plane. In this paper, we focus on the excitation of surface waves propagating on the finite-sized AMC surface, which generates extra resonances and CP radiations for the radiation structures. We predict the surface-wave resonances using a cavity model. In this model, the finite-sized AMC structure is considered as a waveguide resonator. We verify the predicted results computationally using the finite element method-based full-wave electromagnetic solver Ansoft high-frequency structure simulator. The results show that these extra resonances and corresponding CP radiations can be used to broaden the impedance matching and axial ratio bandwidths of the antennas, respectively.

UWB Single Port Log Periodic Toothed Terahertz Antenna Design Based on Graphene Artificial Magnetic Conductor

In this work, a single port exponential tapered toothed log periodic antenna based on graphene artificial magnetic conductor (AMC) is suggested for ultra-wideband (1–10) THz operation. The resonance frequency of the proposed antenna can be tuned by changing the connected DC voltage which leads to variation in the chemical potential of the graphene.The radiating toothed log periodic antenna consists of gold patch placed on 25x25 graphene patches which act as an AMC surface unit. Exponential taper is used to satisfy impedance matching between the antenna and the feeder over the frequency range. The simulation results reveal that 90% of frequency range satisfies when the chemical potential is1eV.

A Low-Profile Dual-Band Dual-Polarized Antenna With an AMC Surface for WLAN Applications

In this letter, a novel low-profile dual-band dual-polarized antenna with an artificial magnetic conductor (AMC) surface for wireless local area network (WLAN) applications is presented. Two sets of bowtie patches are introduced to form two dipoles in ±45° polarizations. Two integrated baluns are used to excite the dipoles. By inserting an AMC surface, the antenna can achieve unidirectional radiation pattern and low-profile characteristics. The height of the proposed antenna is 0.088λ0 at 2.4 GHz. It can provide measured 15.6% (2.36-2.76 GHz) and 9.3% (5.12-5.62 GHz) relative bandwidth, respectively. Port-to-port isolation higher than 22 dB can be realized. Stable radiation patterns with peak gain of 7.2 dBi in lower band and 7.3 dBi in upper band are also obtained. The proposed antenna can be used for multiband base stations for WLAN applications.

Broadband RCS Reduction of Antenna with AMC Using Gradually Concentric Ring Arrangement

This paper proposes a new method to the broadband RCS reduction with the artificial magnetic conductor (AMC) surfaces. The AMC surfaces can introduce a zero-degree reflection phase shift to incident waves. The phase difference between the antenna and AMC structures is 180°. Therefore, the AMC structures can be used to achieve RCS reduction. However, the bandwidth of zero-degree reflection phase of AMC structures is very narrow. In light of this, a novel gradually concentric ring arrangement AMC (GCRA-AMC) which can be applied to achieve the broadband RCS reduction is presented. The simulated and measured results show that the radiation performance of antennas is preserved when the GCRA-AMC is used. The RCS of the antenna with GCRA-AMC has been considerably reduced in a broad frequency band. The largest RCS reduction is more than 17 dB.

Wearable Flexible Reconfigurable Antenna Integrated With Artificial Magnetic Conductor

This letter presents a wearable flexible reconfigurable folded slot antenna. The antenna is composed of a folded slot and a stub where the reconfigurability is achieved by turning a p-i-n diode on and off , which alters the radiation characteristics of the stub. The operating frequency and polarization of the slot and stub are different. Hence, a polarization-dependent dual-band artificial magnetic conductor (AMC) surface is integrated with the antenna to improve its radiation performance and to reduce the specific absorption rate (SAR). The antenna is designed and fabricated on a flexible substrate, and its performance is measured for both flat and curved configurations. The measurements show an excellent agreement with the simulations. To examine its performance as a wearable antenna, it is measured on a human body. Simulations show that the SAR level is reduced when the AMC surface is used as an isolator. The proposed wearable antenna structure can be used for wireless body area network (WBAN) and Worldwide Interoperability for Microwave Access (WiMAX) body-worn wireless devices.

Ultrawideband and Polarization-Independent Radar-Cross-Sectional Reduction With Composite Artificial Magnetic Conductor Surface

A composite artificial magnetic conductor (AMC) surface has been proposed for ultrawideband and polarization-independent radar-cross-sectional (RCS) reduction. Three different AMC units are employed to form the composite surface, which make up of destructive phase difference (180° ± 30°) over a broad frequency range. It is analytically shown that an ultrawideband RCS reduction is achieved from 5.0 to 20.0 GHz for arbitrary polarizations. The RCS reduction value exceeds 10.0 dB almost from 6.0 to 18.4 GHz, resulting in a fractional bandwidth of 101.6%. To verify the proposed design method, the AMC surface specimen is fabricated and measured, and the experimental results agree well with the simulations.

Gain-Enhanced On-Chip Folded Dipole Antenna Utilizing Artificial Magnetic Conductor at 94 GHz

On-chip antennas suffer from low gain values and distorted radiation patterns due to the lossy and high permittivity Si substrate. An ideal solution would be to isolate the lossy Si substrate from the antenna through a perfect electric conductor ground plane. However, the typical CMOS stack up that has multiple metal layers embedded in a thin oxide layer does not permit this. In this letter, an artificial magnetic conductor (AMC) reflecting surface has been utilized to isolate the Si substrate from the antenna. Contrary to the previous reports, the AMC structure is completely embedded in the thin oxide layer with the ground plane above the Si substrate. In this approach, the AMC surface acts for the first time as both a reflector and a silicon shield. As a result, the antenna radiation pattern is not distorted and its gain is improved by 8 dB. The fabricated prototype demonstrates good impedance and radiation characteristics.

Improved Radiation Performance of Low Profile Printed Slot Antenna Using Wideband Planar AMC Surface

In this paper, a novel design of low profile printed slot antenna using wideband artificial magnetic conductor (AMC) is presented with improved radiation performance. For this purpose, the radiating slots with three unequal arms fed by coplanar waveguide are employed for broadening the impedance bandwidth with three resonances. It achieves a wide impedance bandwidth in the measured frequency range of 7.96–12.56 GHz ( $S_{11}\leq -10$ dB) for X-band applications. By loading a novel wideband planar AMC surface as the antenna ground plane, the radiation properties of this printed slot antenna are enhanced. This design includes the measured −10 dB impedance bandwidth from 5.75 to 14.51 GHz (86.48%). The proposed wideband planar AMC design operates at the frequency of 10.15 GHz with ±90° reflection phase bandwidth of 8–12.38 GHz (43.15%). The AMC surface is designed with the $5\times 8$ array of periodic patches which are developed underneath the broadband printed slot antenna. In comparison with the proposed design without AMC, the printed slot antenna loaded with AMC introduces 62.82% size reduction, a bandwidth enhancement of 41.65%, and better impedance matching. It also contributes considerable features like a low profile antenna with unidirectional radiation patterns and an increased gain of more than 10.6 dBi.

AMC‐based broadband bowtie antenna for WIMAX application

ABSTRACTA broadband bowtie antenna with artificial magnetic conductor (AMC) ground is proposed for WIMAX application. Loaded with two parallel open stubs in the upper layer, the proposed bowtie antenna has the merit of broad band. An AMC surface composed of 6 × 9 Jerusalem cross slot unit cells is designed under the bowtie antenna with a distance of 0.1λ, where λ denotes the free space wavelength at 3.0 GHz, for gain enhancement and wide bandwidth on the basis of low profile. Measured results show that, with maintaining a low profile, the composite antenna has a wide bandwidth (return loss 10 dB) from 2.48 to 3.8 GHz (42.04%). The measured peak gain is up to 7.94 dBi, and the maximum cross‐polarization level is −17 dB for both E and H plane. And the measured front‐to‐back ratios are <−19 dB. Both the bowtie antenna and the AMC surface are fabricated and measured. The simulated and the measured results are in good agreement. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2657–2661, 2016

Broadband RCS reduction using a novel double layer chessboard AMC surface

A novel broadband chessboard surfaces with double layer structure to reduce the radar cross-section (RCS) of an object is presented. By combining two artificial magnetic conductor (AMC) cells and a novel structure, 73% frequency bandwidth of −10 dB RCS reduction compared with a metallic plate has been obtained. In order to increase the bandwidth in chessboard structures, boards with high thickness are required, cheaper boards’ thickness are limited. An RO4003 board on an air substrate has been used. This technique, in addition to accommodating the designer with a new parameter, decreases the costs and increases the bandwidth greatly and also simulation results and measurements are in good correspondence.

Wideband circularly polarized low-profile antenna using artificial magnetic conductor

A wideband circularly polarized (CP) antenna with an artificial magnetic conductor (AMC) reflector is presented. Its primary radiation elements are composed of two bowtie dipoles which are arranged orthogonally through double-printed rings to allow easy impedance matching and produce good CP radiation. Planar periodic square metallic plates, which behave as AMC surfaces when placed on a grounded dielectric substrate, are appropriately incorporated with crossed bowtie dipoles to achieve the desired unidirectional radiation, low profile, as well as wideband features. The final design with an overall size of 0.75λo × 0.75λo × 0.11λo (λo is the free space wavelength at 5 GHz) resulted in a measured –10 dB |S11| bandwidth of 54.2% (4.3–7.5 GHz) and a 3-dB axial ratio bandwidth of 33.3% (5–7 GHz). The antenna yields right-hand circular polarization and broadside gain of approximately 7.9 dBic across the CP operating bandwidth.