The techniques of random antenna element distribution and rotation have been proposed to design a low sidelobe and low crosspolarization phased array or reflect array for a long time. In this communication, we demonstrate that the use of randomly rotated (RR) elements can provide random scattering phases and phase center distributions, which can lead to an in-band radar cross section (RCS) reduction for the array. To illustrate the effectiveness of the proposed method, three 8 × 8 circularly polarized (CP) microstrip arrays, 1) the uniform array without rotation; 2) sequentially rotated (SR) array; and 3) RR array, are compared and analyzed. Results indicate that the RCS of the RR array can be reduced significantly, even in the main beam region, while maintaining its high radiation performance.

In this article, we present a low-cost microstrip phased-array antenna, which is composed of electronically reconfigurable elements. The p-i-n diodes' integrated elements have various functions, such as tunable polarization characteristics and adjustable radiation phases. The high sidelobe level (SLL) due to the 2-bit phase shifter can be reduced by a randomly rotated (RR) array element. It is shown that the array can realize electronic beam-steering capabilities and keep -10 to -14 dB sidelobes without tapering. To verify the above theory, an eight-element linear array prototype working at 3 GHz was designed, fabricated, and tested. Numerical simulations and experimental results show that, by controlling the “ON” and “OFF” states of p-i-n diodes, the radiation beam can be controlled to steer in a circular polarization (CP) mode, wherein the scanning angle is up to ±45°. Furthermore, the principle of suppressing the vector scattering field by the opposite phasing cancellation method can achieve in-band radar cross section (RCS) reduction. Simulation results show that approximately 15 dB in-band RCS reduction can be realized for both bistatic and monostatic RCS reduction with an 8×8 array.

In this letter, we investigate a low radar cross-section (RCS) wideband circularly polarized microstrip array antenna co-designed with a high-performance artificial magnetic conductor and frequency selective surface (AMC-FSS) radome. Compared with the absorbent frequency selective radome-based antenna, the proposed co-designed antenna can achieve a relatively low gain loss in an extremely wide frequency range with wideband in-band and out-of-band RCS reduction, due to the introduction of a novel AMC-FSS radome which can achieve low insertion loss and wideband transmission by combining a double-layer miniaturized bandpass FSS and a single-layer chessboard AMC surface. We demonstrate the effectiveness of the proposed AMC-FSS radome and co-designed antenna through simulations and measurements. The results show that the gain deterioration of the co-designed antenna is only 0.42 dB at the central frequency of 4.8 GHz and less than 1 dB in the wide frequency band, ranging from 4.23 to 5.38 GHz with a relative bandwidth of 23.9%. At the same time, the monostatic RCS for a normal incidence is greatly reduced from 4 to 18 GHz.

It is a key problem to constrain the minimum inter-element spacing in the sparse antenna array synthesis. Perturbed compressive sampling (PCS) and convex optimization are two existing sparse array synthesis methods, which have their shortcomings of small spacing between adjacent elements when solving practical problems. In this paper, a new method for sparse planar array synthesis with inter-element minimum spacing constraint is proposed by combining the advantages of PCS and convex optimization. This method solves the problems of small spacing in PCS synthesize results, and long solving time or even invalid for the large-scale array in convex optimization methods. Moreover, the method can ensure that the gain of the sparse array is similar to the uniform counterpart. Numerical results show that the method can maintain the merits of sparsity, PSLL and gain while constraining the minimum inter-element spacing.

In this article, a novel high-efficiency harmonic beamforming technique based on time-modulated arrays (TMAs) with multistate time modulators is proposed. The typical single-sideband TMAs suppress the image harmonic components in the radio frequency (RF) channel, which means low power conversion efficiency, large power consumption, and a major heat dissipation problem. To circumvent these constraints, we present a novel phase modulation (PM) waveform with a linear phase that can be easily constructed using multiple fixed delay lines and a pair of single-pole-multi-throw (SPMT) RF switches. This fundamental PM waveform enables the creation of uniform radiation patterns. Furthermore, two complementary methodologies are proposed for synthesizing more advanced radiation patterns that need nonuniform array weights. One method is to change the linear phase slope of PM waveforms that exhibit sideband radiation but have 100% feeding network efficiency. The other option is to investigate hybrid amplitude and PM (HAPM) waveforms, which suffer from inefficiencies in the feeding network but do not exhibit sideband radiation. Besides, the comprehensive efficiency evaluation formulas have been effectively derived. Simulations have been done to verify its effectiveness.

A low cost, dual circularly polarized (CP) 2-bit antenna working at 10 GHz is reported in this work. The antenna element utilizes a square-ring patch as radiator. By selecting the feeding direction of the T-shaped coupling microstrip line and the position of perturbation corner, the 2-bit phase of 0°, 90°, 180°, 270°, and the CP reconfigurability can be realized. An 8-element linear array is used to verify the beam scanning performance. By controlling the ‘ON’ or ‘OFF’ of the p-i-n diodes, the prototype array can steer the main beam from 0° to 40°. Within these steering beams, simulated and measured results have a good agreement, which verifies the functions of the antenna.