Design of Dual-Band Frequency-Selective Surfaces With Independent Tunability

A design approach for dual-passband frequency-selective surface (FSS) with independent tunability is proposed and implemented. The principle of the proposed design approach is elaborated based on an equivalent circuit model, and it is demonstrated that the construction of FSS unit cell with two independently controlled transmission poles plays a decisive role. Referencing to the proposed approach, a varactor-based polarization-insensitive dual-passband FSS with independent tunability is demonstrated experimentally for the first time. In this prototype, a shunted substrate integrated waveguide cavity (SIWC) like structure is designed to realize electromagnetic isolation and serve as the dc ground for varactors to simplify the dc bias feed network. Simulated and measured results show that both passbands located in L-band and S-band can be tuned independently, and the transmission characteristic of the designed tunable FSS (TFSS) possesses good angle stability.