Design of wideband bandpass frequency selective surface based on the patch resonators and substrate integrated waveguide cavities

In this paper, a new approach for the design of wideband bandpass frequency selective surface (FSS) is proposed based on the microstrip patch resonator and substrate integrated waveguide (SIW) cavity. Originating from the similarity of field distributions between the patch and SIW resonators, the patch resonator is concentrically embedded within the SIW cavity. In this context, resonant modes in both patch resonator and SIW cavity can be generated without enlarging the circuit size. Then, the slotlines are introduced to the ground layer to establish cross-couplings to produce transmission zeros (TZs) for better out-of-band performances. For demonstration, a fourth-order bandpass FSS is constructed, simulated, and fabricated. The measured results agree with the simulated ones, verifying that the proposed design method possesses attractive advantages of low profile, compact size, high frequency selectively, and nice universality.