Noise and IF Gain Bandwidth of a Balanced Waveguide NbN/GaN Hot Electron Bolometer Mixer Operating at 1.3 THz

Journal article, 2018

In this paper, we present the comprehensive characterization
of a waveguide balanced phonon-cooled NbN hot electron
bolometer (HEB) mixer on aGaNbuffer-layer operating at approximately
1.3 terahertz (THz). The measured uncorrected double
sideband noise temperature was as low as 750 K at 1 GHz
intermediate frequency (IF) and 900 K at 4 GHz IF, respectively,
and suggests a noise bandwidth of 7 GHz. Moreover, the IF gain
bandwidth of the HEB itself was deduced from a mixing experiment
with a second monochromatic THz signal source and has
shown a 3 dB roll-off at 5.5 GHz. The contribution of the HEB
mixer on the overall receiver noise temperature was determined
to be in the order of 300 K or 5 hf/k considering losses in the
RF transmission path and the waveguide components as well as
accounting for the receiver conversion loss, which was deduced
from the U-factor method. The achieved performance sets a new
benchmark for futureTHz instruments and emphasizes the technological
readiness of waveguide-based NbN HEB mixers employing
a GaN buffer-layer featuring significantly improved IF bandwidth
without compromising on the receiver’s noise temperature.