Ultra-Wide-Angle Bandpass Frequency Selective Surface

A novel theory is proposed in this article to design a bandpass frequency-selective surface (FSS) with a stable angular response. Based on this theory, the performance of the structure is closely related to its tangential and normal components of permittivity and permeability. Theoretical formulas are derived to realize a high-efficiency transmission response with angular independence. To validate our design concept, an ultrawide-angle bandpass FSS with metallic strips and square patch printed on the dielectric substrate is designed, and it exhibits a characteristic impedance matching for nearly all incident angles from 0° to 80 °. Moreover, varactor diodes are mounted at the center of the square patch, and the transmission window can be tuned by changing the capacitance of the varactors from 6.07 to 6.61 GHz without affecting its ultrawide-angle characteristic. Finally, a prototype of the tunable ultrawide-angle bandpass FSS is fabricated and measured, and the experimental results are in satisfying agreement with the predicted ones.