A Triband Low-Profile High-Gain Planar Antenna Using Fabry–Perot Cavity

A Fabry–Perot antenna using a frequency selective surface layer with wideband and Low RCS for Mm-wave applications

In this paper, an effective approach for mitigating the near-field coupling between four-port circularly polarized (CP) antennas in a 30-GHz multiple-input, multiple-output (MIMO) system is suggested and investigated. This is obtained by incorporating a two-layer transmission-type frequency selective surface (FSS) superstrate based on planar crossed-dipole metal strips. This paper presents a comparison between the mutual coupling when the patches are radiating in free space and in the presence of the FSS layers. The simulated results, when the FSS layers are applied, show an average of 6–12-dB improvement in the isolation between four adjacent CP-MIMO antennas. In addition, an accurate study is carried out on the insignificant reflections produced by the FSS layers to redirect those and also prevent any interference. The proposed $2\times 2$ CP-MIMO antenna along with the superstrate is implemented and tested to validate the simulation results. Experimental results of the coupling and reflection coefficients and axial ratio show an acceptable agreement with the corresponding simulated ones.

In this communication, wide-angle monostatic radar cross section (RCS) reduction of a metal plate is reported. The whole angular range (0°–90°) is divided into three parts according to the different dominant scattering mechanisms. Each dominant scattering mechanism is accurately identified and suppressed effectively. Frequency selective surface (FSS) absorber is employed to reduce the specular echo intensity within the first angular part. The tapered resistive sheets (TRSs) are loading as an edge termination to the metal layer and FSS layer, respectively, providing a slowly varying surface current to taper the transition between the free space and the targets. Significant RCS reduction in the rest two angular parts is achieved. Simulation results clearly show that more than 10 dB monostatic RCS reduction is realized within a wide angular range (0°–10° and 30°–85°) for the frequency band ranging from 1.3 to 2 GHz. Samples have been fabricated and measured in the anechoic chamber, and a remarkable agreement between the simulation and measurement is obtained. The effectiveness of the design is fully verified.

A three-layer frequency selective surface (FSS) tunable absorbing filter is presented. Tunability is achieved through the use, in every FSS layer, of commercially available, low-cost, surface-mount, radio-frequency, varactor diodes. The absorber is experimentally tested in a waveguide over the 1.8–2.4 GHz frequency band. It has the potential to form the basis of a smart microwave absorber.

A broadband metamaterial absorber with a single layer of tantalum nitride (Ta2N3) frequency selective surface layer, printed on a foam substrate, is presented. The proposed design has been numerically examined at the terahertz region. The results have shown that a wideband absorption with absorptivity greater than 90% was achieved in the frequency range 1.17-2.99 THz, and the relative absorption bandwidth was up to 112.97%, which is significantly better than previously reported results. Moreover, the absorber was independent of wave polarization, and a high absorption for a wide range of oblique incidence was achieved. The surface current distribution, the electric field distributions, and the power loss analyses were used to explain the physical mechanism of a wideband absorption. However, the tantalum nitride layer has an important role in the energy absorption. According to the obtained results, the proposed absorber, which is compact and simple to design, has a potential application in evolving broadband terahertz absorbers and sensors.

In this paper, a geometric phase based diffuse scattering metasurface with a high-efficient transmission window is proposed and demonstrated. Meta-atom of this metasurface consists of scattering cancellation layer, dielectric spacer layer and band-pass frequency selective surface (FSS) layer. The binary elements of the metamaterial are meta-atom and its copy rotated by 90° inclined angle. Full-wave electromagnetic simulation indicated that 10 dB RCS reduction band is from 6.4 GHz to 11.3 GHz while the transmission band is 15.1 GHz with 0.3 dB insertion loss. Sample of this metamaterial was fabricated and measured to validate the simulation results.

This paper presents a dual-polarized angle-selective surface with three layers of frequency-selective surfaces. The hexagon-shaped pattern is chosen to be the unit cell of this design, which shows similar performance with different incident angles for both TE- and TM polarizations. A formula is derived based on the odd-even mode theory to achieve bandpass condition under the normal incidence. Simulation results show that a passband $(|S_{21}|\gt -1$ dB) from 0° to 7° and a stopband $(|S_{21}|\lt -20$ dB) from 25° to 70° are observed at 7 GHz for both polarizations.

In this paper, a high gain ultra wideband (UWB) antenna by employing a single layer frequency selective surface (FSS) as a reflector is presented. The impedance bandwidth of the proposed antenna is 155% (1.9 to 15.2 GHz) with peak gain 5.9 dBi. Further the gain of the proposed UWB antenna has been improved by placing a frequency selective surface (FSS) array reflector underneath the UWB antenna. The unit element of FSS is a circular loop structure and further modified in to 5X5 element array. The UWB antenna with FSS reflector showed the enhancement in gain from 5.9 dBi average peak gain to 9.2 dBi and it's almost stable in the higher band. The comparative analysis of gain and radiation patterns of antenna with and without FSS has been discussed to observe the effect of FSS on the antenna performance. The full wave EM simulation has been carried out by using CST MWS.

Based on the research basis of single-layer cross-shaped frequency selective fabrics, the electromagnetic transmission characteristics of double-layer and three-layer cross-shaped frequency selective fabrics were explored in this paper. The frequency selective fabrics with different multilayer structures and specific-sized conductive units were designed, and then prepared by the computer engraving method and tested using the free-space method. The results show that the single-layer sample is less affected by the polarization mode of the electromagnetic wave, while the effect of the incidence angle is slightly larger. For the frequency selective fabric samples with the same frequency selective surface layers, the frequency selective characteristics of the double-layer samples are more ideal than those of the single-layer samples, while the electromagnetic loss of the three-layer samples is large and the narrow-band transmission characteristic is weakened. For the frequency selective fabric samples with the complementary frequency selective surface layers, the double-layer sample mainly shows band-pass characteristics and the narrow-band transmission characteristics are better than the single-layer sample. The three-layer sample of ‘patch + aperture + patch’ presents band-pass characteristics, and the ‘aperture + patch + aperture’ sample generates resonance at multiple frequency points, but the resonance peaks are all less than –10.00 dB, meaning that the sample presents full shielding characteristics in the test frequency band. The equivalent circuit model was built to explore the electromagnetic transmission mechanism, revealing the fabric type and structure, and the conductive unit type and size will affect the equivalent impedance of the frequency selective fabrics, thus further influencing the electromagnetic transmission characteristics.

A Fabry-Perot cavity antenna (FPCA) system with high efficiency is proposed. The design consists of a source antenna with a frequency selective surface (FSS). The source antenna is an aperture coupled microstrip slot antenna with cavity backing. The FSS is a square aperture with rectangular unit cells. The E-field in the near and far field is compared for the FPCA system and the source antenna without the FSS (i.e. source antenna only). The FPCA has low phase variation of approximately 10° in the E-plane compared to high sinusoidal phase variation of 90° of the source antenna. The far-field gain of the FPCA system is 11.3 dB, which is a 4.5 dB improvement of the source antenna gain. The aperture efficiency of the FPCA system is 84% compared to the source antenna efficiency of 30%.

This paper describes a variable-reflection-angle meta-surface that can control a scattering pattern by sliding one layer of a double-layered frequency selective surface. A reflection angle within a range of approximately 2° to 35° is obtained in the proposed structure according to the unit cell analysis of the meta-surface. A scattering pattern is calculated by FDTD analysis, and the peaks are in good agreement with the range.

Low-Pass Three Layer Frequency Selective Surface

In the paper, a tri-band angularly stable frequency selective surface (FSS) with controllable resonances for electromagnetic shielding is proposed. Different from traditional single-layer structure, the FSS proposed is based on cascaded structure that creates three adjustable blocking bands around frequency 5.93 GHz, 7.33 GHz and 9.17 GHz, respectively. The designed FSS has a low profile with thickness of λ0/100, where the λ0 represents wavelength of the first band-stop resonance frequency. Besides, the proposed FSS exhibits stable frequency response up to 70° with respect to different polarizations. Therefore, this FSS is flexible and can be used in electromagnetic shielding field where needs conformal screen. To investigate and understand the operating mechanism better, a equivalent circuit model (ECM) is deduced and given in the Section 2, the calculated results match the full-wave EM simulation results perfectly. Finally, a prototype of this FSS is fabricated and measured, the measurement results are in accordance with the simulation results.

In this paper, a low profile, ultrathin, wide passband, polarization insensitive, wide angular stable frequency selective surface (FSS) is proposed. The structure is realized on a two-sided copper on Roger’s RT 5880 substrate with 0.51 mm thickness. The top layer design consists of a combination of slotted circle with quad arcs along with cross bars at the center with diagonal tilts at the corner. On the bottom layer, an elliptical-shaped patch is placed at the center. This elliptical patch at the bottom layer of FSS helps to realize the wide pass-band response. The pass-band bandwidth ranges from 8.45 to 9.45 GHz centered at 8.96 GHz. The proposed FSS is polarization insensitive. The structure provides angular stability till 45° of incident angle for Transverse Electric (TE) and Transverse Magnetic (TM) modes of operation. The prototype of FSS is fabricated with an array of 10 x 10 unit cells. The simulated and measured results are found to be in good agreement.

ABSTRACTIn this letter, a low profile circularly polarized wearable antenna with the appearance of a button on clothing for Wi‐Fi and WLAN applications is presented. The radiating elements of the antenna are made of copper sheet while a transparent acrylic fiber sheet material is used as substrate and fed by a coaxial line through the ground plane. The proposed antenna is simulated by Ansoft high frequency structure synthesis finite element method‐based (HFSS FEM)‐based EM simulator and has been optimized to operate within the Wi‐Fi and WLAN frequency bands (5250–5850 MHz) with center frequency of 5.25 GHz. A split ring‐shaped slot‐based frequency selective surface (FSS) is designed to enhance the gain of the proposed antenna. The peak gain of the antenna is found to increase from the conventional antenna gain of 2.1 to 5.1 dBi with the superstrate along with a bandwidth enhancement of 290 MHz. The composite FSS antenna is fabricated and the maximum measured gain of 5.1 dBi matches well with theoretical value. The antenna gets miniaturized around 34% by the slits with its circular polarization characteristic well maintained. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1033–1038, 2015