A Tunable Metamaterial Frequency-Selective Surface With Variable Modes of Operation

A reconfigurable miniaturized-element frequency-selective surface (FSS) is presented in this paper. A standard waveguide measurement setup is used to evaluate the performance of the design. The proposed FSS consists of two periodic arrays of metallic loops, with the same periodicity, on either side of a very thin dielectric substrate. The tuning of the reconfigurable surface is shown numerically to be possible by incorporating tuning varactors into the structure. Using varactors on both layers, a reconfigurable frequency response is achieved, which has two modes of operation: bandstop and bandpass. In addition to two completely different modes of operation, the center frequency, as well as the bandwidth of the response can be tuned independently. Frequency tunability with a constant bandwidth over 3-3.5 GHz is shown. A bandwidth tuning at a fixed center frequency is also demonstrated. Simulation results are verified experimentally by fabricating prototypes of the design at S-band loaded with lumped capacitors. To demonstrate the tunability, different pairs of fixed-valued capacitors, as opposed to varactors, are used in a waveguide measurement setup to avoid difficulties associated with biasing varactors in the waveguide.