Design of High-Efficiency Transmitarray With Beam-Steering and Low-Scattering Characteristic

This article introduces a hybrid design method for high-efficiency absorbing reconfigurable transmitarray (ARTA). By cascading an absorbing layer with a 2-bit reconfigurable layer, the transmission unitcells can realize the frequency response characteristic of an absorbing-transmissive–absorbing (A-T-A). Specifically, the frequencies with an absorption rate exceeding 80% are within the ranges of 3.3–5.1 and 7.8–9.4 GHz, while the frequency range with transmission exceeding –3 dB spans from 5.69 to 5.92 GHz. Meanwhile, the transmission phase can be adjusted among four states: 0°, 90°, 180°, and 270°, enabling beam steering of ARTA. Compared to designs for nonreconfigurable transmissive arrays, our design methodology necessitates the satisfaction of absorbing performance under different phase states. For validation, a prototype sample, comprising a $12 \times 12$ array structured with five metallic layers and four dielectric layers, sandwiching an air layer in between, has been fabricated and tested. The measurement results demonstrated high radiation performance with a peak gain of 21.6 dB and aperture efficiency of 33.3% at 5.85 GHz. The BW-1 and BW-3 dB were 0.2 and 0.6 GHz, respectively. $\pm 60^{\circ }~2$ D-scanning was achievable and when the beam is directed at 0°, the sidelobe levels (SLLs) in the E-plane and H-plane are –17.3 and –18 dB, respectively. Under normal incidence of an x-polarized wave, the –8 dB monostatic RCS reduction bandwidths covered 32.1% (3.4–4.7 GHz) for lower band and 10% (8.5–9.4 GHz) for upper band. The ARTA by this hybrid design methodology represents an attractive solution for addressing electromagnetic compatibility issues and for low-detectability applications.