Reconfigurable reflectarray antennas (RRAs) have rapidly developed with various prototypes proposed in recent literatures. However, designing wideband, multiband, or high-frequency RRAs faces great challenges, especially the lengthy simulation time due to the lack of systematic design guidance. The current scattering viewpoint of the RRA element, which couples antenna structures and switches during the design process, fails to address these issues. Here, we propose a novel radiation viewpoint to model, evaluate, and design RRA elements. Using this viewpoint, the design goal is to match the element impedance to a characteristic impedance pre-calculated by switch parameters, allowing various impedance matching techniques developed in classical antennas to be applied in RRA element design. Furthermore, the theoretical performance limit can be pre-determined at given switch parameters before designing specific structures, and the constant loss curve is suggested as an intuitive tool to evaluate element performance in the Smith chart. The proposed method is validated by a practical 1-bit RRA element with degraded switch parameters. Then, a 1-bit RRA element with wideband performance is successfully designed using the proposed design process. The proposed method provides a novel perspective of RRA elements, and offers a systematic and effective guidance for designing wideband, multiband, and high-frequency RRAs.

With the rapid development of reconfigurable transmitarray antennas (RTAs), a lot of antenna prototypes have been proposed in literatures. It is noticed that all 1-bit RTA elements utilize at least two switches to realize 1-bit transmission phase difference. Hence, a question arises: is it possible to design a 1-bit reconfigurable transmitarray element with a single switch? In this letter, three-port network theory is employed to prove that a single-switch RTA element CANNOT realize both high transmission efficiency and 1-bit phase tuning ability simultaneously. Furthermore, we also prove that it is impossible to realize a 1-bit reconfigurable reflectarray antenna (RRA) element with polarization conversion that uses only one switch. However, based on two-port network equivalence, a 1-bit RRA element without polarization conversion is possible by using a single switch.

Terahertz reconfigurable reflectarray antennas (RRAs) hold significant promise for next-generation wireless communication systems by enabling dynamic beam control to mitigate severe path loss at high frequencies. This work presents a Complementary Metal-Oxide-Semiconductor (CMOS)-based RRA for terahertz amplitude control using tunable split-ring resonators. First, a terahertz switch in standard 65 nm CMOS process is designed, tested, and calibrated on the chip to extract the equivalent impedance, enabling precise RRA element design. Next, a reconfigurable element architecture is presented through the co-design of a split-ring radiator, control line, and a single switch. Experimental characterization demonstrates that the fabricated RRA achieves 3 dB amplitude variation at 0.290 THz with <8.5 dB element loss under 0.8 V gate bias. The measured results validate that the proposed single-switch topology effectively balances reconfigurability and loss performance in the terahertz regime. The demonstrated CMOS-compatible RRA provides a scalable solution for real-time beamforming in terahertz communication systems.

This paper presents a compact-size switch operating in the frequency range of 285 to 310 GHz, employing the standard 65-nm CMOS process. The terahertz performance of the switch is enhanced through a custom-designed inductive loop that resonates with the parasitic capacitance of the switch. Additionally, the floating-body technique is employed to mitigate leakage. The probe tests and the Thru-Reflect-Line (TRL) calibration tests are conducted to extract the equivalent impedance of the switch within the operating frequency range. Comparative experiments are conducted to evaluate the impact of using the two techniques on the switch's performance. Furthermore, a comparison between simulation and measurement results of the proposed switch is performed. Equivalent circuit models are introduced based on the physical structure of proposed switch, and the fitted parameters are presented. The fabricated switch, with a compact footprint of merely 30 μm × 40 μm, achieves a measured insertion loss of 1.5 dB in the ON state and more than 6.0 dB of isolation in the OFF state within the operating frequency range and can be effectively employed as a tunable component in metasurface applications.