Varactor-tunable Bandpass Frequency Selective Surface with Wide Tuning Range

A varactor-tunable bandpass frequency selective surface with wide tuning range is presented in this paper. The proposed Frequency Selective Surface (FSS) is composed of three stacked metallic layers. In the top and bottom layers, four varactors are loaded between the cross-shaped patch and the inductive wire grid of the FSS unit cell, respectively. The wire grid in each layer is connected by a via, which forms a bias network. The advantage of this network is that no additional DC bias network is needed, which can effectively reduce the frequency offset caused by DC bias. The passband can be tuned by changing the capacitance of varators loaded in the unit cell. Full-wave simulations show a 59% wide tuning range from 11.4 to 6.2GHz with an insertion loss between 0.3-2.3dB by changing the varator capacitance from 0.1 to 0.4pF.