LOW-NOISE BROAD-BAND FIXED TUNED SIS WAVE-GUIDE MIXERS AT 660 AND 800GHZ

We present measurements and simulations of mixer performance around 66 0 GHz and around 800 GHz. We use Nb-Al2O3-Nb tunnel junctions with are as of 0.9 mu m(2) and 0.7 mu m(2), and RA-products of 14.5 Omega(mu m) (2) and 13 Omega(mu m)(2) for 660 GHz and 800 GHz, Both junctions have an integrated tuning structure made of niobium that consists of a ser ies resonant stub and a quarter lambda transformer, The waveguide mixe rblock has no additional adjustable tuning elements. It contains just a waveguide cavity and a substrate channel across it, A horn is carefu lly adjusted to the cavity and flanged to the block. The measured rece iver noise temperatures from 630-690 GHz are below 190 K with a best v alue of 120 K at 655 GHz. From 780-820 GHz they are below 950 K with a best value of 780 K at 792 GHz. When the operating temperature is red uced from 4.2 K to 2.5 K, a reduction in noise temperature from 830 K to 660 K is observed at 810 GHz. The mixer performance is simulated us ing the quantum theory of mixing. The simulated performance shows a fa irly good agreement with the measured one.