Wideband MgB2 Hot-Electron Bolometer Mixers: IF Impedance Characterisation and Modeling

In this paper, we present a method for low-signal S11 parameter vector measurements of a cryogenic device in the microwave frequency range. In particular, the intermediate frequency (IF) impedance of MgB
₂
hot-electron bolometer (HEB) mixers was investigated over a frequency range of 100 MHz to 10 GHz. A new cryogenic calibration technique, which employs the HEB as a calibration kit and requires two consecutive thermal cycles, was developed for this purpose. The real part of measured IF impedance showed a strong correlation with the differential resistance (dV/dI) obtained from the dc I-V curves, whereas the imaginary part was capacitive for almost the entire frequency range.