On the frequency response symmetry of diode mixers

A mixing process is symmetrical when the conversion loss and group delay are equal between a downconversion and the corresponding upconversion. It is shown here by measurement that diode mixers have some degree of response asymmetry. Simulations show that the response asymmetry is caused by the voltage-variable junction capacitance of the mixer diodes. The response asymmetry sets a limit on the accuracy of three-mixer and other techniques to derive the frequency response of individual mixers.