Mixing experiments have been performed at frequencies from 4 to 20 GHz on Nb thin‐film superconducting hot‐electron bolometers varying in length from 0.08 to 3 μm. The intermediate frequency (IF) bandwidth is found to vary as L−2, with L the bridge length, for devices shorter than √12 Le−ph≊1 μm, with Le−ph the electron‐phonon length. The shortest device has an IF bandwidth greater than 6 GHz, the largest reported for a low‐Tc superconducting bolometric mixer. The conversion efficiencies range from −5 to −11 dB (single sideband, SSB). For short bridges, the mixer noise temperature is found to be as low as 100 K (double sideband, DSB), with little length dependence. The local oscillator power required is small, ≊10 nW. Such mixers are very promising for low‐noise THz heterodyne receivers.

Topics
Phonons, Oscillators, Signal processing, Thin films, Electromagnetic radiation detectors
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The power coupling to the device in the normal state from the cold rf input was measured to be above 90% from 0.1–12 GHz. The match is expected to remain this good to above 20 GHz.
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A cooled dc bias tee (Anritsu K250) was used. The dc load line was 20 Ω.
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For devices D and E, the dominant noise at low IF is due to thermal flucuations, but it is much too small to measure at 1.5 GHz.
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© 1996 American Institute of Physics.
1996
American Institute of Physics
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