Tunable Bandpass FSS With Wideband Tuning and Low Insertion Loss Based on Waveguide Array

In this paper, we present a tunable bandpass frequency-selective surface (FSS) with wide tuning range. The FSS is composed of a metallic rectangular waveguide array implanted in the double-sided printed circuit board (DSPCB) and an array of embedded varactors with bias network in the backside of the DSPCB. The waveguide array has a frequency-selective transmission peak due to tunneling effect and the transmission frequency is tuned by changing the capacitance of varactors through different bias voltages. One advantage of this configuration is that the varactors together with the bias network are designed on the same layer, which can effectively reduce the overall thickness into only 0.006λc (λc is the free-space wavelength at the highest transmission frequency). On the other hand, the insertion loss associated with the parasitic resistance of varactors is greatly decreased, owing to the novel integrated design of biasing lines with varactors and the nearly-full-metal waveguide array. A prototype is fabricated and measured, showing that by changing the varactor capacitance from 0.12 pF to 1 pF, the passband exhibits a 2.32:1 frequency tuning range from 5.8 GHz to 2.5 GHz with an insertion loss of 0.2 dB-2.6 dB. A polarization-insensitive FSS is also studied in simulations.