Abstract
A modulator based on switchable frequency selective surface (FSS) is presented. It is designed to operate both as a free space and waveguide modulator for future high speed communication applications. Rectangular loop aperture geometry has been used for FSS design to provide modulation for one polarisation only i.e. TE or TM. Switching has been achieved using two PIN diodes placed across the aperture at 180 degree interval. Negative DC biasing is provided from the back while positive DC biasing is provided from the front of FSS structure. To minimize the effect of bias line on the overall frequency response, it has been placed orthogonally to the principle axis of FSS. A pin is attached from back to front to provide electrical connection between the two ends. Theoretically, about 20 dB transmission loss can be achieved at centre frequency, when the PIN diodes are switched between OFF and ON states. This switchable FSS can be used as an amplitude shift keying modulator.