Design of a Ka-band upconverter using a heterojunction bipolar transistor

Heterojunction bipolar transistors (HBTs) are attracting interest around the world, finding use in power amplifiers and low phase noise oscillators. There is little information, however, on the performance of HBT devices as mixers, specifically as upconverters in the transmitter path. Using a proprietary HBT model implemented on Libra^TM by the Communications Research Centre, the HBT is investigated for its suitability as a mixer. A single-ended microwave monolithic integrated circuit (MMIC) upconverter is designed with the IF and LO fed through the base and emitter, respectively, thereby eliminating the need for a diplexer. The simulated upconverter (IF=3.6 GHz and RF=30.1 GHz) yields a conversion gain greater than 2 dB over a bandwidth of 300 MHz. At the RF port, the IF, LO and image frequency isolations are 19 dB, 18 dB and 13 dB respectively, while at the IF port, the RF, LO and image frequency isolations are all greater than 40 dB