A design of a microwave absorber based on frequency selective surface resonating in X-band having ultrathin thickness, polarization controlled behavior, and increased absorption bandwidth has been reported. The reported absorber having its unit cell embodied of multiple resonating structures which includes conventional square, circular, and butterfly shaped resonators resulting in three absorption apexes at 9.44, 10.00, and 10.53 GHz (all in X band) with 99.9%, 99%, and 95.1% of absorptivity obtained at the frequencies of resonances. It demonstrates a wide full width at half maximum having 1.48 GHz as bandwidth, at the expense of using an ultrathin substrate of 0.0096 λ0, where λ0 is the wavelength with respect to lowest resonating frequency, i.e. 9.44 GHz. The unit cell is fourfold symmetric exhibiting independence about the absorber’s polarity, as well as, it behaves stable over the outspread angle up to 45 degrees for both transverse magnetic and transverse electric polarized wave under sloped incident angle. The absorption behavior has been demonstrated by plotting the distribution of surface-currents and electric fields at the frequencies of resonance. The fabricated prototype of the presented design is tested at X-band and the obtained results concur with the simulated results.

We present the design for a thin planar microwave absorber depicting near unity absorption over a wide bandwidth. The absorber consists of a single layer of resistive frequency selective surface inkjet printed over a paper substrate and suspended over a grounded foam. We have been able to achieve 99.99% absorption of normally incident radiations from 9.7 to 11.74 GHz at an extremely low level of −40 dB absorption bandwidth. The proposed absorber is thin (0.22λ0 at the center frequency), polarization-insensitive, and presents −10, −20, −30, and −40 dB fractional bandwidths as 89.83%, 55.41%, 33.30%, and 19.03%, respectively. It is worth mentioning that the design of an absorber with such steep slopes is highly stringent and requires special attention. Finally, we have experimentally demonstrated the perfect broadband absorption characteristics with a fabricated prototype.

Metamaterial lenses are appealing thin alternatives to conventional dielectric lenses. In this contribution we describe their design and application in two exemplary 77 GHz automotive radar sensors operating in monostatic and bistatic modes. The frontends are built around commercially available MMICs and small feed antennas are used in coordination with the six-layer printed circuit board-based realizations of metamaterial lenses. The design follows the principles of dielectric lenses, while the required local phase shift is obtained from a set of metasurface bandpasses. Their design uses a novel interpolation procedure to extract layout parameters for a given phase shift. Despite the small structural sizes due to the high frequency, the fabricated frequency-selective surfaces show very good performance in the required frequency range. Verification measurements were conducted on single bandpasses as well as on metamaterial lenses mounted on the radar frontend. The results agree very well with the simulation and confirm the applicability of thin lenses operating at mm-wave frequencies for automotive radar applications.

In this study, a compact modified circular ring-based circuit analog absorber (CAA) is proposed. It comprises a resistor-loaded frequency selective surface (FSS) underneath an FR-4 substrate, and the other end is terminated with a perfect electric conductor (PEC) separated by an air-spacer. The proposed design shows a minimum −10 dB reflectance from 10.55 to 36.03 GHz (25.48 GHz bandwidth and 109.4% fractional bandwidth) with two dips at 13.5 GHz and 35.23 GHz having reflectivity −17.18 dB and −24.9 dB, respectively. The existing four-fold circular symmetry architecture shows insensitivity for different polarization angles under normal incidences and up to 45° stability for Transverse Electric (TE) and Transverse Magnetic (TM) modes under oblique incidences. The proposed cell is compact with a periodicity of 0.193λL, and a thickness of 0.09λL, where λL is the free-space wavelength corresponding to the lowest frequency of the absorption band. The novelty of the design lies in the topology of using an underneath FSS to take advantage of effective permittivity control for both broader bandwidth and better angular stability. To demonstrate the ability of the proposed design, a 28 GHz microstrip patch antenna prototype is fabricated, and its radar cross section (RCS) is measured after loading with the absorber. A 15.15 dBsm RCS reduction is observed in comparison with the PEC. The authors strongly believe that the proposed design has potential applications such as RCS reduction and radio-frequency energy harvesting.

The paper has proposed a multilayer, polarization rotation featured, low radar cross-section (RCS) antenna using electromagnetic band-gap (EBG)-based frequency selective surface (FSS) at 8.25 GHz. Cross-shaped EBG unit cells offer zero reflection phase and −25 dB reflection magnitude at 8.25 GHz. The FSS layer consists of eight cross-shaped EBG unit cells sandwiched between two substrates to offer high absorptivity at the desired band. The circular patch antenna resonating at 8.25 GHz is placed on the top substrate having a lower dielectric constant. Four circular-shaped patches are etched at the four corners of the top layer and are coupled with two feed lines which are aligned 90° to each other at the bottom layer and interconnected diagonally to achieve polarization rotation. The proposed antenna offers a gain of 6.72 dB and an in-band RCS of −21.4 dBsm. Incident energy is backscattered into eight directions separated by angle ϕ = 45°. The proposed antenna has the RCS reduction band of 7.7–9.4 GHz. It offers normalized polarization rotation ratio more than 0.8 within the −40° to 40° angular region at the frequency band 8–8.5 GHz. The measured result using the fabricated prototype agrees well with the simulated one.

A low-profile, wideband dual-polarized 1 × 2 multiple-input-multiple-output (MIMO) antenna with frequency selective surface (FSS) decoupling technique is presented. Low profile is realized with two different artificial magnetic conductor (AMC) cells out of which one operates at 3.5 GHz and other with dual band at 3.1 and 4.5 GHz. The proposed antenna height is maintained at 0.125λ0 which is significantly reduced when compared with the conventional perfect electric conductor (PEC) ground plane. Wideband dual polarization is enabled by two pairs of bow-tie antenna elements surrounded by a square ring placed in the orthogonal orientation. To mitigate the near-field coupling in 1 × 2 MIMO an FSS wall is constructed with wide band stop characteristics from 2.85 to 4.75 GHz. Measured results show by inserting FSS wall vertically, coupling reduction is improved by 27 dB over the existing coupling and the antenna exhibits a bandwidth of 57.14% (2.95–4.95 GHz) for VSWR<2 with port isolation of more than 25 dB for entire band of operation.

The radiation characteristics of the microstrip antenna (MSA) on the frequency selective surface (FSS) based absorbing layer is presented in this paper. It is observed that an absorbing layer placed between the MSA configuration and the ground plane helps in controlling the radiation characteristics of the antenna. It not only reduces the back lobe but also reduces the beamwidth and gain of the antenna simultaneously. This is because the absorbing layer absorbs some amount of power radiated by the antenna in both forward and backward directions. The proposed design is simulated using Ansys HFSS electromagnetic simulation software and the results are validated by comparing it with the results obtained from the equivalent circuit approach as well as experimental results. The effect of absorber on radiation characteristics of the radiator demonstrates its potential use in suppressing the radiation from the printed circuit board traces.

In this paper, a sandwiched type frequency selective surface (FSS) is designed and analyzed. The design procedure and operating principle is given based on the equivalent circuit model. The proposed FSS includes two identical layers of periodic metallic arrays, which are separated by a foam layer. In each layer of the periodic array, the unit cell is composed of a gridded-triple square loop structure. The FSS provides three pass-bands, in which a flat band response is presented. Three bands are separated by one or two transmission zeros, which leads to a sharp rejection on both sides of each pass-band. The central frequencies of the three pass-bands are 7.0, 10.9 and 14.0 GHz. To verify the simulated results, a prototype of the FSS is fabricated and measured. The simulated results agree well with the measured ones. This work can be used in area of a radar stealth or satellite communication system.

In this paper, a simple synthesis technique to obtain the geometrical parameters of the modified circular ring for angular and polarizations (perpendicular and parallel) stable frequency selective surface (FSS) has been discussed. The geometrical parameters of the modified circular ring FSS structure have been achieved using the proposed synthesis technique, which is based on the equivalent circuit (EC) approach. In addition to this, the numerical analysis is also discussed to determine the values of EC parameters, which depends on the basic system level characteristics such as frequency of operation and reflection/transmission coefficients. The analytical results are supported using the full-wave three-dimensional electromagnetic (EM) simulators such as CST Microwave Studio and Ansoft HFSS. The sensitivity of the structure to the perpendicular and parallel polarized EM wave up to 50° angle-of-incidences (AOIs) has been discussed. The stability over different AOI is attributed to the appropriate thickness of the structure with its small unit-cell dimensions. We have also fabricated and experimentally tested the proposed FSS structure.