# 1-Bit Reconfigurable Transmitarray Antenna with Out-of-Band RCS Reduction +
###### Abstract  
Stealth reconfigurable transmitarray antennas (RTAs) are essential components in wireless communication and radar detection systems. Therefore, in this study, we propose a 1-bit RTA with out-of-band radar cross-section (RCS) reduction. The antenna consists of an absorptive frequency selective transmission (AFST) layer and RTA layer separated by air. Specifically, the AFST layer achieves out-of-band RCS reduction and in-band transmission utilizing the first three resonant modes of a bent metallic strip with a centrally loaded resistor. Meanwhile, the RTA layer adopts a receiver-transmitter structure with an active receiving dipole and a passive orthogonal transmitting dipole. 1-bit phase shift is achieved by alternating two pin diodes integrated on the active dipole to reverse its current direction. To evaluate the proposed design, a 16 \(\times\) 16-element prototype was designed, fabricated, and measured. For scattering, the bandwidth of 10 dB RCS reduction was about 52.5% and 43.8%, respectively. For radiation, the measured gain was 20.1 dBi at 7.5 GHz, corresponding to an aperture efficiency of 12.7%. The gain loss of beam scans to \(\pm\)60\({}^{\circ}\) was about 5 dB in both two principal planes. os +
Footnote †: This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ([[https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/)]([https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/))). Footnote †: This article is a revised and expanded version of a paper entitled [Design of a low RCS 1 bit electronically reconfigurable transmitarray antenna], which was presented at [International Conference on Microwave and Millimeter Wave Technology (ICMMT), Qingdao, China, 2023]. Various approaches have been explored to realize low-RCS transmitarray antennas. These include the use of a resistive sheet, fixed bandstop frequency selective surface (FSS), and adjustable bandpass FSS with phase-shifting capability to achieve absorption-type low-RCS transmitarray antennas [10]. In building on this, a diffuse reflection low-RCS transmitarray antenna was realized using anti-reflection dielectric columns of different heights and a bandpass FSS as a phase shifter [11]. In addition, an asymmetric resonator with resistance was used to obtain an absorption-transmission-absorption response, and the transmission phase was controlled by rotating an open resonant ring to achieve a 1-bit phase change [12]. The same design concept of integrating an absorptive frequency selective transmission (AFST) layer and phase modulation layer was also implemented in [13; 14; 15]. However, these transmitarray antennas do not contain switching devices or phase shifters, so once the prototype is fabricated, the radiation beam is fixed and cannot be quickly controlled through the electrical signal. Compared to traditional RTAs, 1-bit RTAs offer several advantages, including low cost and electrically controllable radiation characteristics. As a result, they are better suited for modern high-integration application systems that require various functions. Previous research on RTAs has primarily focused on more polarizations [16; 17], increasing the beam scanning angle [18], simple structures [19], and higher phase control accuracy [20; 21]. However, there has been limited research on reducing the RCS of RTAs. In [22], 1-bit beam scanning and RCS reduction were achieved in different polarizations, but the structures were relatively complex. In our previous work [23], the AFST and RTA layer were combined to realize out-of-band RCS reduction and in-band beam scanning. However, the RCS reduction band was narrow and only worked under single polarization. To address this technology gap of simultaneously achieving dual-polarized wideband out-of-band RCS reduction and in-band beam scanning, we propose a 1-bit RTA with wideband out-of-band RCS reduction. The element comprises an AFST layer and an RTA layer.