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.

The design and experiment of an electronically reconfigurable bidirectional spatially-fed array are presented, which combines the functionalities of reconfigurable transmitarray (TA), reflectarray (RA), and transmit-reflect array (TRA). First, we demonstrate a novel bidirectional unit cell composed of a tunable resonant layer between a pair of orthogonally oriented metal gratings. Two positive-intrinsic-negative (PIN) diodes are integrated into the tunable resonant layer to achieve the 1-bit phase resolution in either transmission or reflection mode. Based on the proposed unit cell, a 16 × 16-element array arranged in a square grid, which can be controlled independently by a field programmable gate array (FPGA)-based digital control circuit, is excited by a linearly-polarized horn to show the beam steering ability of reconfigurable TA and RA. To realize TRA function integration with the bidirectional beam independent steering simultaneously, the method based on superposition of the aperture fields (SAF) on the aperture is used. In SAF design, the entire aperture is divided into transmission and reflection modes co-existing, and the arrangement and phase distribution are optimized by particle swarm optimization (PSO) algorithm to achieve minimum sidelobe levels (SLLs) and peak gain of bidirectional beam. The measured results of the prototype demonstrate that the antenna can steer bidirectional beam both in simultaneous and time division operating modes, which is not reported to the best of the authors’ knowledge. Our proposed method opens a new avenue for the design of high-performance multifunctional reconfigurable antenna systems.

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.

Inspired by the recent progress of metasurfaces, a novel wideband and high-efficiency electronically reconfigurable transmitarray (TA) is presented that can enable two-dimensional (2-D) beam steering and multiple beam mode switching in a digital manner. The proposed unit cell consists of a reconfigurable anisotropic metallic resonator, which locates between a pair of orthogonally oriented subwavelength metal gratings. One-bit phase quantization is obtained by controlling the ON or OFF state of two positive-intrinsic-negative (p-i-n) diodes integrated on the anisotropic metallic resonator layer. To choke the radio frequency (RF) signal effectively, a bias layer is connected by the metallic via hole to the center of the resonator, where the electric field is minimal. The simulated results show that the proposed unit cell can achieve a low insertion loss of 1 dB from 9.3 to 10.9 GHz for two phase states. Then, the radiation performance of a 10 $\times\,\,10$ element array fed by a pyramidal horn antenna is theoretically calculated, simulated, and measured. The measured maximum gain is 19.1 dBi at 10.0 GHz with an aperture efficiency of 25.8% and a 3 dB gain bandwidth of 15.9%. The measured results demonstrate the 2-D beam scanning capability within the 50° range.

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.

A quad-polarization reconfigurable reflectarray (RA) antenna, which can work in horizontal polarization (HP), vertical polarization (VP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP) modes with simultaneous large-angle beam scanning capability, is designed and experimentally verified. Under the traditional view at the element level, at least 2-bit phases are required because a 90° phase shift step is needed for conversion from linear polarization (LP) to circular polarization (CP). In this work, we found that the extra phase shifts (90°/-90°) can be achieved by changing the global reference phase of the 0/1 coding arrangement in the spatially-fed architecture, while 1-bit phase resolution is used in the element level. As verification, a square patch with four slots loaded with two positive-intrinsic-negative (PIN) diodes is exploited as a RA element with 1-bit phase independent control of dual-linear polarization. Then, the RA aperture contains 16 × 16 elements, where 512 PIN diodes are integrated to control each state independently by a field programmable gate array, excited by a linearly-polarized horn is developed and fabricated. Besides, the superposition of the aperture field approach is used to optimize CP radiation performance, especially the axial ratio (AR). The measured results of the prototype demonstrate the simultaneous multi-polarization reconfigurable and the beam steering capability, where scanning beams are up to 60° in horizontal and vertical planes. The proposed low-lost design is believed to be a promising candidate for mobile communication and cognitive radar applications.