A quasi-elliptical bandpass frequency selective surface with low-profile and miniaturization characteristics

A low-profile and miniaturized frequency selective surface (FSS) with dual-polarized bandpass characteristics is proposed in this article. The FSS is a second-order structure with two layers separated by an air spacer, achieving two transmission poles (TPs) and two transmission zeros (TZs) at both sides of the TPs. Using the miniaturized structure, the physical dimension of the element is reduced to 0.09 lambda x 0.09 lambda, where lambda is the free-space wavelength at the center frequency. Thus, the structure exhibits stable performance with respect to different incident angles. The overall thickness is 0.053 lambda, which is much thinner than alternative second-order FSSs using the traditional cascading technique. This feature makes it a candidate to be applied in low frequency bands with long wavelengths. In addition, the operating principle of the proposed structure is analyzed by using the equivalent circuit method (ECM) and the surface current distribution is also given. Finally, a prototype is fabricated and measured to validate the simulated results.