Second-order plasma enabled tunable low-profile frequency selective surface based on coupling inter-layer

This paper presents a second-order reconfigurable frequency selective surface based on tunable plasma and inverter interlayers. The proposed design concept starts with a second order spatial filter with the ability to deliver selective filtering response for arbitrary FSS thicknesses. Furthermore, low-profile design and inverter layers provide simple implementation solution in designing tunable spatial filters. In this paper, we demonstrate second-order low-profile band pass spatial filter operating at S-band with fast in-band shielding switch capability within 20 to 100 ns for the protection of electromagnetic systems. The proposed tunable spatial filter is integrated with discrete plasma shells strategically located to effectively switch the transfer function of the filter. The coupling layer, a metallic strip wire serves dual purpose in not only controlling the thickness of the filter but also as a biasing network for the active components. To validate the proposed technique, a prototype tunable filter operating at 3 GHz with periodicity and overall thickness in the order of λ0/10 has been fabricated and measured inside a waveguide. Simulation and measurement results are proven to be in good agreement.