Effects of the Diode Junction Capacitance on the Conversion Loss of Microwave Mixers

The theory of the frequency down-converters, which use sinusoidally driven exponential junction diode, is reviewed here with the purpose of investigating the effects of the junction Capacitance on the conversion loss. The analysis deals With single-ended mixers, both in the and configurations. Their performances are compared with those obtained from the same configurations of mixers using a purely resistive (PR) exponential diode, in cases of both short-circuited and open-circuited image frequency. This comparison shows that the junction capacitance modifies strongly the behavior of the single-ended mixer compared tothe case of purely resistive diodes. It is pointed out that, when the junction capacitance may not be neglected, and the image frequency is either open- or short-circuited, good performance can still be achieved from a sinusoidally driven mixer. On the contrary, the sinusoidally driven mixer, which Operates better than the mixer when the effect of the junction capacitance may be neglected, is strongly deteriorated, and it becomes worse than the mixer.