Inductively-Coupled Miniaturized-Element Frequency Selective Surfaces With Narrowband, High-Order Bandpass Responses

We introduce a new technique for designing miniaturized-element frequency selective surfaces (MEFSSs) with narrowband, bandpass responses of order N ≥ 2. The proposed structure is composed of two-dimensional periodic arrays of subwavelength inductive wire grids separated by dielectric substrates. A simple equivalent circuit model, composed of transmission line resonators coupled together with shunt inductors, is presented for this structure. Using this equivalent circuit model, an analytical synthesis procedure is developed that can be used to synthesize the MEFSS from its desired system-level performance indicators such as the center frequency of operation and bandwidth. Using this synthesis procedure, a prototype of the proposed MEFSS with a second-order bandpass response, center frequency of 21 GHz, and fractional bandwidth of 5% is designed, fabricated, and experimentally characterized. The measurement results confirm the theoretical predictions and the design procedure of the structure and demonstrate that the proposed MEFSS has a stable frequency response with respect to the angle of incidence of the EM wave in the ±40° range for both TE and TM polarizations of incidence.