Limitations of Microwave and Millimeter-Wave Mixers Due to Excess Noise

Previous analytical work on microwave and millimeter-wave mixers concentrated on circuit aspects, utilizing for the analysis a simple noise model consisting of shot and thermal noise sources at a constant temperature. However, measurements show that the excess noise created in the diode by hot electrons, intervalley scattering, and traps at the metal-semiconductor interface can be important, especially in millimeter-wave mixers. In this paper, the method of calculation of mixer noise performance in the presence of excess noise is given and its influence discussed for room-temperature, as well as for cooled, mixers.