Dual-Passband Reconfigurable FSS With Concurrently Tunable and Connected Passbands

In this article, a dual-passband reconfigurable frequency-selective surface (DRFSS) with continuous and connected passband tuning ranges is proposed. First, an equivalent circuit analysis of the DRFSS is conducted to evaluate the impact of design parameters on the two passbands’ transmission performance. In addition, the influence of varactor diodes on the tunable bandwidth is analyzed. Second, based on the analysis, a design method is proposed. Third, a composite unit cell structure is developed, incorporating two parallel groups of identical varactors for simultaneous dual-passband tunability, with an isolated bias network ensuring polarization-independent performance. Finally, prototypes for parallel-plate waveguide (PPW) and free-space measurements are fabricated and measured. Experimental results agree well with simulations, verifying the superior performance and feasibility of the proposed DRFSS. Key features include a tunable relative bandwidth (RBW) of up to 119.0%, high-transmission efficiency within the passbands, and the distinctive characteristic of connected tunable passbands. In addition, the design can be adapted for independently tunable passbands as needed.