A 320GHz low drive level sub-harmonic mixer based on quantum barrier junctions

A sub-harmonically pumped (n=4) down conversion mixer, employing single quantum barrier junction in place of a Schottky pair, is designed and simulated using the symbolically defined device capability in ADS and transmission line optimisation using HFSS prior to fabrication. The performance in terms of conversion loss and LO power requirements are estimated and compared with state-of-the-art Schottky diode mixers. The intent was to explore a low drive level mixer with high conversion efficiency (minimum conversion loss) for potential use at sub-millimetre wave frequencies, where the device parasitic´s, such as junction capacitance and series resistance have a marked effect on performance and where LO pump powers are often weak. The performance is explored via a design operating at 320GHz and showing a signal side band (SSB) conversion loss with 5.7dB, with only -9.5dBm (≈0.1mW) of LO power. The conversion loss is maintained below 10dB, even when using -8dBm to -11dBm of LO drive level, and the eventual aim of the work is to realize a similar design with an operating frequency of 640GHz for meteorological studies.