Active Frequency Selective Surfaces for Tunable Bandpass Filter and Switching Between Transmission and Absorption Band

In this paper, a polarization-insensitive tunable active frequency selective surface (AFSS) has been designed. The unit cell is engraved on a single-layer substrate with a 2D periodic repetition of 4-splits meandered square ring resonator (MSRR). Four varactor diodes are placed at the 4-splits of the MSRR with thin connected metal strips on both sides of the substrate for biasing the diode. The proposed AFSS exhibits a bandpass filter response, whose resonance frequency can be tuned by changing the capacitance of the varactor diodes. Full wave simulation of the FSS displays the frequency tuning range from 1.58 to 2.58 GHz (48.1 %). An additional substrate layer with slotted inductive grids printed at the back is stacked at the bottom of the first AFSS for switching between transmission and absorption. Two FSS layers are separated by a thin air gap. The switching is achieved by changing the ON/OFF states of the four PIN diodes placed within slot gaps of the metal grid.