Bandpass Frequency Selective Structure With Wideband Spurious Rejection

This letter presents a miniaturized bandpass frequency selective structure (FSS) based on stepped-impedance resonator (SIR) for spurious suppression. The proposed FSS consists of a periodic array of two-layer printed circuit boards and a number of inserted metallic rods and plates, where inductor-loaded SIRs are constructed based on the propagation modes in each unit cell. By properly selecting the impedance ratio of the SIRs and the inductance of the inserted metallic rods, the FSS can provide a bandpass response with two transmission poles in the passband and a very wide stopband capable of suppressing multiple spurious modes in the upper band. An equivalent circuit model is established to explain its operating principle, and it is analyzed by using the even-odd-mode analysis method. As an example, a prototype of the proposed FSS is designed, fabricated, and tested. Good agreement between simulated and measured results verifies the design concept of the bandpass FSS.