Miniaturized-Element Bandpass FSS by Loading Capacitive Structures

Abstract

A bandpass frequency-selective surface (FSS) element loaded with capacitive structures is proposed to miniaturize FSS unit cell size. In the FSS design, the capacitive structure, implemented by convoluted slot grids (CSGs), is introduced to increase the equivalent capacitance of the bandpass FSS, thus leading to a lower resonance frequency. The FSS unit cell size is then reduced accordingly. To validate this design concept, a double-layered bandpass FSS consisting of convoluted slot dipole and CSG structures is designed to provide a unit cell size as small as $0.035\lambda _{0} \times 0.035\lambda _{0}$ , where $\lambda _{0}$ refers to the resonance wavelength in the free space. Equivalent circuit of this FSS is established for explaining the resonance mechanism and modeling the frequency performance. Finally, a prototype of the proposed FSS is fabricated and measured. The measured results exhibit the stable filtering response under different polarizations and incidence angles (up to 60°), which also agree well with those obtained by full-wave simulations.