Influence of Temperature Variations on the Stability of a Submm Wave Receiver

Radio astronomy requires SIS mixers and receivers with very high stability. The goal for the total power stability of the ALMA receivers is 1x10 over 1 second. The SIS mixer is one of the most critical components in the receiver signal chain determining stability. Most changes in mixer noise and gain are due to variations of its operating conditions. In this paper we present accurate measurements of SIS mixer noise and gain variations with respect to physical temperature, operating point and local oscillator power changes. We use an ALMA band 9 prototype waveguide mixer – developed at NOVA-SRON − working in the 600-720 GHz frequency range. Intermediate frequency coverage of this mixer is 4-11 GHz. A 4-12 GHz isolator was used between the mixer and IF amplifier. The physical temperature of the mixer was varied from 2.5 K to 6 K in steps of 0.05 K and the mixer parameters were measured. Based on our measurement data we provide an estimate (derivatives) of the influence of mixer operating temperature on gain and noise temperature for different LO frequencies.