A Low-Profile Varactor-Tunable Bandpass Frequency Selective Surface With Angular Stability Property

A low-profile varactor-tunable bandpass frequency selective surface (FSS) with angular stability is presented in this article. The FSS comprises two metallic layers printed on the opposite sides of a thin substrate. The rotationally symmetrical meandered metal patch in each layer in combination with metallic vias is the feed network of the varactor diodes, which has been optimized to achieve miniaturization and obtain suitable coupling capacitance C-s. Moreover, the feed network is arranged to be rotationally symmetrical to ensure polarization independence. An equivalent circuit model and the synthesis procedure are provided to simplify the design of the FSS. The designed resonance frequency is tuned from 3 to 4.55 GHz when the bias voltage varies from 6 to 20 V. The thickness of the structure is 0.005 lambda(0), where lambda(0) represents the wavelength of the lowest resonance frequency. Furthermore, the effect of structural parameters on the angular stability of the FSS has been reported. The proposed FSS is angularly stable at 3-4.55 GHz for the incident angle up to 70(degrees) under both TE and TM waves. A prototype is manufactured, and the measured S-parameters under normal and oblique incidence verify the effectiveness of the proposed design.