FSS modulator for future high speed communication applications

A modulator based on a switchable frequency selective surface (FSS) is presented. The FSS can be designed to operate either as a free space or a waveguide modulator for possible future high speed communication applications. A rectangular loop aperture geometry is used for the FSS design in order to provide modulation for one polarisation only i.e. TE or TM. Switching can be achieved using two PIN diodes placed across the aperture at 180 degree interval. Negative DC biasing is provided from the back-side while positive DC biasing is provided from the front of the FSS structure. To minimize the effect of bias line on the overall frequency response, they have been placed orthogonal to the principle axis of the FSS. As an example at 31.5GHz, a transmission discrimination of >;30dB is predicted, when the PIN diodes are switched, enabling this switchable FSS to be used for amplitude shift keying modulation.