Abstract

An extended analysis is presented for the excess noise of GaAs-Schottky-Diodes in a mm-waveguide-mixer. A mixer simulation program includes the effects of nonlinear capacitances, arbitrary embedding impedances, non ideality of microwave diodes and all kinds of noise generated in the diode. The determination of the diode capacitance is established in an empirical way. With the measurement of both, the noise at 94 GHz and the conversion loss, it is possible to find a new characteristic of the capacitance versus voltage. This differs from the commonly used square root function. Based on measurements of the noise temperature for different currents in the frequency range of 100 MHz to 94 GHz a noise model of the diode is established and compared to conventional noise theory: In the frequency range below 2 GHz the noise temperature runs through a maximum with respect to diode current; with the frequency increased the maximum decreases and is shifted to higher currents. This effect can be modeled by a current dependent time constant in the trapping noise formula. Finally measurements at an original 94 GHz mixer were done to verify the theoretical results including the extensions mentioned above. Calculated and measured values of conversion loss and noise temperature agree in an excellent manner.