Inherent signal losses in resistive-diode mixers

A time-domain scattering matrix technique is proposed for the characterization and analysis of the type of diode mixer used for RF and microwave receivers. The method is applicable to single-diode mixers in which the intermediate frequency is a small fraction of the signal and local oscillator frequencies with the network impedance essentially constant over the band which includes the signal, local oscillator and image frequencies. The results provide a three-frequency scattering matrix which describe the mixer's performance as though it were a three-port network. The method is then extended to include the effects of suppressing the image response by the insertion of a band-rejection filter into the input RF line. Good agreement is obtained with the classical frequency-domain approach.