A 290–310 GHz Single Sideband Mixer With Integrated Waveguide Filters

A 290-310 GHz Schottky diode based subharmonic mixer with integrated, low loss, impedance matching waveguide cavity filters is presented in this paper. This mixer was designed for use in a 300 GHz communication system with a 20 GHz intermediate frequency band centred at 15 GHz. Image rejection of the 260-280 GHz lower sideband, as well as impedance matching, was achieved using an integrated third-order filter in the RF waveguide. The conventional coupling matrix was used to design the filter even though the impedance presented to the RF port was complex and frequency dependent. The mixer was measured to have: 1) single sideband conversion loss of 9-10 dB across the upper sideband, with a mixer noise temperature of 2000-2600 K; 2) a return loss at the RF port better than 12 dB, with three filter reflection zeroes (poles) distinguishable; and 3) a sideband rejection ratio from 13 to 25 dB, demonstrating the RF filter's excellent performance in terms of impedance matching and filtering.