Noise performance of a balanced waveguide NbN HEB mixer utilizing a GaN buffer-layer at 1.3 THz

Paper in proceedings, 2018

We report on the initial measurement results of a balanced waveguide phonon cooled NbN mixer employing a 5.5 µm thin GaN membrane, which was operated at frequencies around 1.3 THz. The uncorrected DSB noise temperature amounts to approximately 750 K at 1 GHz IF and increases to only 900 K at 4 GHz IF, which was deduced from the standard Y-factor measurement technique. The recorded IF spectrum from 0.5 GHz to 8 GHz suggests a measured noise bandwidth of approximately 7 GHz owing to the employment of a GaN buffer-layer, which promotes the single crystal growth of NbN films and provides high phonon transparency, thus lowering the phonon escape time. We emphasize with the implementation of a waveguide balanced receiver scheme and using NbN/GaN mixers the possibility to extend the operational IF range of phonon cooled NbN HEBs, yet providing low noise performance.