Analysis and Design of a High-Transmittance Performance for Varactor-Tunable Frequency-Selective Surface

This article aims to achieve a high-transmittance varactor-tunable frequency-selective surface (FSS). First, the impedance condition for the high-transmittance FSS is deduced. Next, a square-slot FSS loaded with varactors, which owns the empirical formulas for equivalent circuit parameter extraction, is selected to demonstrate the proposed method for realizing a high-transmittance varactor-tunable FSS. Several conclusions are deduced and verified through the full-wave simulation. To illustrate the effectiveness of the proposed method, two FSSs operating at the same frequency are designed. The simulation and measurement results show that the FSS with the higher transmission rate follows the deduced conclusions. Note that the transmission rate of the varactor-tunable FSS is more than 77.8% ( S
₂₁
= 1.09 dB) from 4.84 to 5.9 GHz when the bias voltage applied to the varactors is tuned from 5 to 20 V. Compared to the reported tunable FSSs, the varactor-tunable FSS achieved in this article obtains the highest transmission rate over the tunable transmission band.