Gain stability analysis of a millimeter wave superconducting heterodyne receiver for radio astronomy

Gain fluctuation of a receiver system for radio astronomy determines the ultimate observation sensitivity. To well understand the system stability property it is desirable to set apart of the gain fluctuation of each subsystem from the overall instability. This is a fundamental approach leading to further improvement of system stability. In this paper, we introduce a method to allow decomposition of the Allan variance of the fractional gain variation of a millimeter wave superconducting heterodyne receiver system. By this means, the contributions of SIS mixer and the cascading amplifier stages to the overall gain instability can be clarified. This method is also applicable to any linear system with cascading stages.