Measurement of gain and noise in SIS quasiparticle mixers
The superconductor-insulator-superconductor (SIS) quasiparticle tunnel junction is used for millimeter wave heterodyne mixing. Junctions fabricated from different materials are operated in both the classical and quantum regimes and the results are compared with the quantum theory of mixing. A 30-40 GHz test was constructed that allows measurements of the noise temperature of SIS mixers with an accuracy of +/-1K or better. The new feature of this technique is the use of novel variable-temperature cryogenic loads. This accuracy is sufficiently high to allow quantitative comparisons to be made for the first time with the quantum shot noise theory. Mixers consisting of single junctions and series connected arrays of junctions were tested. Conversion gain higher than +4 dB and noise temperatures as low as 3.8 +/- 1K have been measured in single junctions mixers. This noise temperature is only 1.5 times the quantum limits hf/(k.ln2) approx. 2.5 K at 36 GHz. In addition, harmonic mixing of a 36 GHz signal with an 18 GHz local oscillator with mixer conversion gain near -3 dB was demonstrated.
- Research Organization:
- California Univ., Berkeley (USA)
- OSTI ID:
- 5137923
- Country of Publication:
- United States
- Language:
- English
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