Noise comparison of biased and unbiased even-harmonic Josephson mixers

A numerical analysis of the excess noise parameter in biased and unbiased even-harmonic Josephson mixers is presented. It is shown that the unbiased operation has a much lower noise temperature than the biased operation. This is attributed to the exclusion of noise down-conversions due to the odd-harmonic mixing and the Josephson mixing. The results indicate the preferable use of the unbiased mixers as highly sensitive detectors of submillimeter waves.