Analysis of the Broad IF-Band Performance of MgB2 HEB Mixers

We present an experimental study of gain and noise bandwidths in superconducting MgB₂ hot-electron bolometer (HEB) terahertz mixers in a 0.1-20 GHz intermediate frequency (IF) range. At an elevated temperature and with a 90-GHz local oscillator (LO), we measure a gain bandwidth of 13-14 GHz, which is the first accurate data for ultrathin MgB₂ films. The output noise spectrum has its maximum in the 100-200 K range, depending on the temperature (or the LO power) and the bias point, and its spectrum also confirms the gain bandwidth data obtained with the mixing experiment. Using both the gain and the output noise spectra, we obtain the mixer input noise temperature, which is nearly constant up to 20 GHz. Using the measured data and the HEB mixer theory, we argue that noise bandwidth in the current MgB₂ HEB mixers is ~30 GHz.