Development of the cryogenic load for 1.1–1.4 mm sideband separating SIS-mixer

This paper describes the design of a waveguide load for a cryogenic sideband separating receiver based on SIS mixers for the 1.1–1.4 mm range. The load is designed as a metal insert in the center of the waveguide. The insert is based on 125 $\mu$m thick quartz substrate with a deposited 8 nm thick NiCr film, which has a resistance of about 250 $\Omega$/sq. Measurements demonstrate the variations of the film resistance to be within 5 percent while temperature changes from 300 to 4.2 K. Simulations show that the load reflection level can be expected to be less than -35 dB in the 220–330 GHz range.