Bandpass 3-D Frequency Selective Surfaces Based on Microstrip resonator Unit Cell

In this work, a novel bandpass three dimensional frequency selective surface (3-D FSS) based on microstrip resonator unit cell is proposed. Using bandpass filter synthesis theory, we have designed a second-order 3-D FSS with one transmission zero on both upper and lower skirt respectively. The synthesis and design process of the proposed 3-D FSS structure are described in detail. It is obvious that this 3-D FSS structure has good second-order filtering characteristics, which has a passband at 5.0 GHz with -20 dB fractional bandwidth of 11.2%, from 4.71 to 5.27 GHz. The return loss of the passband is less than 0.4 dB. The proposed method is also suitable for the design of higher order 3-D FSS structures.