| Summary: | Supra-THz heterodyne mixers generally have higher conversion loss compared to the millimetre-wave mixers.
Hence, the overall receiver noise temperature becomes increasingly dominated by the first-stage semiconductor
low noise amplifier (LNA), which still struggles to achieve quantum-limited noise performance. Here, we aim to
develop a Josephson junction travelling wave parametric amplifier (JTWPA) that can achieve high gain over broad
bandwidth but with better noise performance to replace these Intermediate Frequency (IF) amplifiers. JTWPAs
are typically considered not suitable for astronomical receivers due to their low power handling capability.
However, the critical current of the Josephson junctions (JJ) can be easily engineered to match the output
power of the front-end detectors. Nevertheless, this may results in the requirement of a higher number of JJs
as the junction inductance is in reverse relation with the critical current. Therefore, in this paper, we aim to
explore the different design parameters required for developing a JTWPA with a dynamic range compatible for
readout a Superconductor-Insulator-Superconductor (SIS) mixer, as an example. Here, we present two JTWPA
models that are suitable for the objective, one requiring 3,142 Nb/Al-AlOx/Nb junctions with a maximum gain
of 23 dB, and the other with a lower gain at 16 dB but requires only 1,317 JJs. We then compare the SIS
receiver noise performance utilising these JTWPAs with that of using a conventional high gain High Electron
Mobility Transistor (HEMT) amplifier. We show that we can improve the receiver sensitivity significantly by
either cascading two 23 dB gain JTWPA or using a combination of a 16 dB gain JTWPA and a HEMT amplifier.
We conclude that the former option more suitable for large detector array applications as it completely replaces
the high heat dissipation HEMT amplifiers; while the latter option is favourable at this stage for low pixel count
application as it is easier to fabricate a lower number of junctions JTWPA.
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