Design and testing of frequency-selective surfaces on silicon substrates for submillimeter-wave applications

A new class of frequency-selective surfaces (FSSs), to be used as quasi-optical filters for harmonic suppression in submillimeter-wave frequency multipliers, is proposed and experimentally verified. The FSSs consist of two-dimensional aperture arrays and are made from microstructured aluminum on electrically thick, high-resistivity silicon substrates. This leads to a very good mechanical stability, reasonably low insertion loss, and permits manufacture of the structure by using standard processes available from the semiconductor industries. This paper presents the design, fabrication, and testing of two sets of prototypes, the former with a passband at 300 GHz and a stopband at 450 GHz and the latter with a passband at 600 GHz and a stopband at 750 GM. For both frequency ranges, FSSs with rectangular slots and with dogbone-shaped holes have been designed by using the method of moments/boundary integral-resonant mode expansion method. The effect of ohmic and dielectric losses has been determined by using the commercial code HFSS. Several prototypes have been fabricated, and measured by terahertz time-domain spectroscopy and continuous wave measurements, showing high reproducibility of the machining process, insertion loss between 1.0 and 1.6 dB, and stopband attenuation larger than 30 dB. Finally,. we demonstrate that the incidence angle can be used as a degree of freedom for fine tuning the stopband, without practically changing the frequency response in the passband.