Multiloop mixer circuits

It is shown that multiloop mixers using resistance diodes pumped at one frequency, but with various phases, have a minimum loss of 3 dB if the terminations are `broadband¿, and if the circuit loops have self and mutual impedances which are pure resistances at the intermediate frequency. The latter condition prohibits phase shifters in the intermediate-frequency paths, and therefore implies that these are necessary in successful low-loss broadband mixers. It is further shown that, for the minimum loss of the mixer to approach 0 dB, the circuit must have image-rejection properties.