A polystyrene cap for matching a silicon lens at millimeter wavelengths

A polystyrene cap for a silicon lens has been fabricated by thermal molding. The cap is 0.5mm thick, and it acts as a quarter-wave matching layer at 94GHz. The measured performance from 75GHz to 170GHz agrees with theory. The reflection loss at 94GHz is reduced by 1.5dB. This is an economical way to make a millimeter-wave anti-reflection coating. This makes a monolithic circuit with a gallium-arsenide substrate and a silicon lens much more attractive than before. The total absorption and reflection loss for a linch diameter lens with the cap should be 1.1dB.