Multilayer mesh filters for quasi-optical beamsplitting applications

This paper describes the progress made in developing low loss quasi-optical beamsplitting frequency selective surfaces (FSSs), where the spatial demultiplexing of very closely spaced frequency bands is required. The objective of this work is to produce a filter that can separate the bands 316.5-325.5 GHz and 349.5-358.5 GHz with ≤0.5 dB insertion loss and ≥20 dB isolation. Experimental devices have been manufactured, consisting of a rectangular array of 460×15 μm slots etched in a 84 μm thick 30 mm diameter flexible membrane, which when coated in aluminium forms a single perforated conducting screen.