Effect of the Critical and Operational Temperatures on the Sensitivity of ${\hbox{MgB}}_{2}$ HEB Mixers

In this paper, we present a study of the noise and the gain of MgB2 hot-electron bolometer mixers with different critical temperatures (Tc) and at various operation temperatures. At a local oscillator (LO) frequency of 1.63 THz the minimum input receiver noise temperature (Tr) was 700 K with a gain of -18 dB for a device with a Tc of 8.5 K. For a device with a Tc of 22.5 K the corresponding values were 1700 K and -19 dB. For the latter device the Tr was 2150 K at a bath temperature of 12 K, which is not achievable with Nb-compound based HEB mixers. We present and compare different methods for measurements of the HEB mixer gain and the output noise.

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