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
Z
and
Y
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
Y
mixer. On the contrary, the sinusoidally driven
Z
mixer, which Operates better than the
Y
mixer when the effect of the junction capacitance may be neglected, is strongly deteriorated, and it becomes worse than the
Y
mixer.