A Three-Layered Adjustable Frequency-Selective Surface for Wireless Applications

Abstract

A three-layered adjustable frequency-selective surface (FSS) is proposed and investigated. The FSS consists of a main resonator in the middle layer and two subresonators in the upper and lower layers of a sandwich structure. The resonant frequency can be varied by shifting the upper and lower layers symmetrically. This has the advantages that the same frequency characteristics can be obtained in both vertical and horizontal polarizations and that its fabrication is easy, eliminating the need for electronic elements such as varactor diodes to control capacitance, although the FSS is not suitable for situations that require real-time tuning. This article confirms that the resonant frequency can be varied from <inline-formula> <tex-math notation= LaTeX >$f_{0}$ </tex-math></inline-formula> to <inline-formula> <tex-math notation= LaTeX >$1.7f_{0}$ </tex-math></inline-formula> in a microwave band which covers multiple wireless bands, with good angular stability in both vertical and horizontal polarizations, by shifting the upper and lower layer overlaps by up to 1.8 mm. Note that <inline-formula> <tex-math notation= LaTeX >$f_{0}$ </tex-math></inline-formula> is the lowest resonant frequency, and the size of a unit cell is varied from <inline-formula> <tex-math notation= LaTeX >$0.066\\lambda $ </tex-math></inline-formula> to <inline-formula> <tex-math notation= LaTeX >$0.125\\lambda $ </tex-math></inline-formula>. Also, the adjustment capability and the angular stability of an FSS fabricated by using a silver inkjet printer are experimentally demonstrated, by simply stacking and shifting the three films.