Wideband modulator for high switching speed frequency synthesiser

This paper describes a single sideband suppressed carrier modulator intended to produce fine frequency stepping on the output of a broadband synthesiser, operating from below 1 GHz to greater than 5 GHz. The digitally synthesised local oscillator in the 100-200 MHz range is in principle also capable of working broadband. The modulator consists of a 90° coupler, a hybrid of 5 GaAs MMICs and a Si 400 MHz direct digital frequency synthesiser. The GaAs hybrid contains 2 active 180° splitters, 2 balanced FET mixers and a combining amplifier. An output of 0 dBm is obtained from the modulator with better than 20 dB rejection of the unwanted carrier and sideband