Frequency-Selective-Surface-Based Mechanically Reconfigurable Terahertz Bandpass Filter

Frequency-tunablefilters are in demand for applications requiring high spectral selectivity. To this end, frequency-selective surfaces (FSSs) have been widely applied for spatial filtering, where varactors well serve the purpose for electronic reconfiguration at microwave frequencies. For terahertz applications, however, varactors are unavoidably lossy owing to their relatively small cross section required to yield small values of capacitance. In this work, we propose a terahertz bandpass multilayer FSS with a finesse around 20, with 80% power transmission. Its operation frequency is mechanically tunable in a 40% frequency range by varying an interlayer spacer thickness. The experimentally validated bandwidth is 31% due to the limitation in measurement apparatus, and the power transmission is above 75%. The filter is insensitive to misalignment and can maintain tunability under oblique angles of incidence. This proposed filter outperforms a series of notable reconfigurable filters available in the literature in terms of tunable range and insertion loss. The proposed design is among the first few reconfigurable terahertz filters, and the design methodology can be readily applied to other FSS-based structures.