In this research, a checkerboard metasurface based on a novel physical mechanism, optimized multielement phase cancellation (OMEPC), is proposed for greatly expanding the bandwidth of radar cross-section (RCS) reduction. More basic meta-particles and, in particular, the variable phase difference between them, greatly increase the ability to control electromagnetic (EM) waves. Interactions between multiple local waves produced by the basic meta-particles at multiple frequencies sampled in a super-wide frequency band are manipulated and optimized simultaneously to achieve phase cancellation. The proposed metasurface can achieve 10 dB RCS reduction in a super-wide frequency band from 5.5 to 32.3 GHz with a ratio bandwidth (fH/fL) of 5.87:1 under normal incidence for both polarizations. Furthermore, the RCS reduction is larger than 8 dB from 5.4 to 40 GHz with a ratio bandwidth of 7.4:1. The metasurface also has a good performance under wide-angle oblique incidences. The optimal meta-particle distribution is found to obtain super-wideband bistatic RCS reduction. The theoretical analysis, simulation and experiment results are in good agreement and verify the ability and capability of the proposed mechanism.

A dual-polarization frequency-selective rasorber with two absorptive bands at both sides of a passband is presented. Based on the characteristic mode analysis, a circuit analog absorber is designed using a lossy FSS that consists of miniaturized meander lines and lumped resistors. The positions and values of resistors are determined according to the analysis of modal significances and modal current. After that, the presented rasorber is designed by cascading of the lossy FSS and a lossless bandpass FSS. Equivalent circuits of the frequency-selective rasorber are modelled, and surface current distributions of both FSSs are illustrated to explain the operation mechanism. Measurement results show that, under the normal incidence, a minimum insertion loss of 0.27 dB is achieved at a passband around 6 GHz, and the absorption bands with an absorption rate higher than 80% are 2.5 to 4.6 GHz in the lower band and 7.7 to 12 GHz in the higher band, respectively. Our results exhibit good agreements between measurements and simulations.

Based on polarization conversion and destructive interference, a novel monolayered metasurface is proposed for ultrawideband monostatic and bistatic radar cross section (RCS) reductions for both copolarization and cross polarization. Unit cells share a simple asymmetric double arrow shape, but with variable geometry parameters, correspondingly with different polarization conversion capabilities and different reflection coefficients. The particle swarm optimization (PSO) algorithm and array theory are combined to optimize and select appropriate parameters for unit cells. The optimized unit cells (O-cells) simultaneously realize the polarization conversion and destructive interference to reduce copolarized RCS. In addition, mirrors of these O-cells (M-cells) are adopted to achieve the complete destructive interference to reduce cross-polarized RCS. Therefore, the total monostatic RCS can be greatly reduced. To improve the bistatic RCS reduction, random distribution of unit cells is carefully designed to realize diffusion patterns. In both the simulation and measurement results, a 10 dB monostatic RCS reduction at the normal incidence is achieved from 7.5 to 22.5 GHz (100% bandwidth). Furthermore, good specular and bistatic RCS reduction performances under oblique incident waves are also obtained. The proposed methodology opens up a new route for ultrawideband RCS reduction.

In this paper, the working mechanism of a wideband absorber designed with an adjustable and highly selective notch band is studied, in which the narrow notch band is independently controlled by the lower lossless layer of the absorber, while the upper lossy layer loaded with lumped resistors realizes absorption. We present two instances with geometrically controlled and electrically controlled notch bands, respectively. Without decreasing absorption performance, the notch position can be flexibly adjusted throughout the entire frequency band by simply modifying the dimension of the lossless frequency-selective surface (FSS) or changing the capacitance of the varactor, i.e., using geometric control or electrical control. The narrow notch band allows two wide absorption bands to be retained on both sides; therefore, good stealth performance is still guaranteed. Equivalent circuit models (ECM) are proposed to further explain the principle. The frequency-domain simulation, ECM, time-domain simulation, and experimental results are in good agreement and validate the adjustability and high selectivity of the notched absorbers. At the end of this paper, an FSA-backed monopole antenna is simulated and measured, which clearly illustrates that these FSAs can serve as the ground plane for antennas and realize out-of-band RCS reduction.

This letter presents an absorptive/transmissive frequency selective surface (ATFSS) with wide absorption bands at both sides of a passband. A double-layer structure consisting of a lossy FSS and a lossless FSS was employed. The lossy and lossless FSSs were designed based on tripole loops and tripole slots, respectively. The tripole loops and slots were constructed as hexagonal periodic structure. The tripole loops equated to a series-parallel circuit, and exhibited lossy feature after they were loaded with lumped resistors, which were used to absorb the incident wave at lower and upper absorption bands. Surface current distributions were illustrated to explain the operation mechanism. A prototype of the proposed ATFSS was fabricated and measured. Our results showed good agreement between measurements and simulations. Measurement results showed that a passband with a center frequency of 5 GHz and a minimum insertion loss of 0.35 dB was obtained. Out of the passband, absorption rates higher than 80% were obtained at a lower absorption band, from 2.66 to 4.5 GHz, and at a higher absorption band, from 5.66 to 8.56 GHz.

Electromagnetic metasurfaces are structured surfaces consisting of a thin array of subwavelength elements with engineered scattering properties, thus providing a promising means of holographic display by controlling the field distributions. However, the existing metasurface holography has limited capabilities in achieving three-dimensional (3D) fields with simultaneous features of high spatial resolution and energy efficiency due to the design methods. In this work, we present a transmissive metasurface to achieve polarization-dependent field distributions in 3D space with both high resolution and efficiency. In the design, a new method that utilizes dyadic-Green’s-function (DGF) as the rigorous propagator is used. With the method the sources and fields are linked directly and can be located on arbitrary 3D points with the intermediate spaces being equal or unequal. The design is successfully validated by full-wave simulations and experimental measurements. The broadband simulation results indicate that the design has a bandwidth of 0.8 GHz. This work demonstrates a feasible and simple route of field synthesis for real-world applications that require high resolution, high efficiency, and 3D scenarios.