Freestanding submillimetre wave FSS technology

In this paper we report on two methods of fabricating Frequency Selective Surfaces (FSS) which are designed to give a polarisation independent band pass filter response centred at 321 GHz. One of the designs is based on metal encapsulated polymer while a later version uses silicon on insulator (SOI) as the structural material. The fabrication of the devices was carried out in a clean room laboratory using precision micromachining and plating processes. These include the use of reactive ion etching (RIE) to pattern the individual slots and deep RIE to remove the substrate underneath. This process yields a Freestanding FSS which can be duplicated to form multilayer structures with enhanced filtering performance. Quasi-optical transmission measurements in the 290 GHz - 360 GHz range yield spectral transmission coefficients which are in close agreement with the numerical predictions.