Quasi-reciprocal mixer as an absolute vector signal standard at microwave frequencies

A reciprocal mixer has the potential to extend an absolute calibration of magnitude and phase relationships at baseband to an absolute calibration at microwave frequencies. Unfortunately, recent publications have shown that mixers are not in general reciprocal devices. The authors' tests have shown that the up- and down-conversion transmission responses for a mixer change with time and temperature. The ratio of the up- and down-conversion transmission responses, however, can be remarkably constant with time and temperature for some mixers. The authors refer to this ratio as the characterised non-reciprocal ratio (CNR) for the mixer. By using a new calibration circuit, they are able to utilise this CNR for a quasi-reciprocal mixer and provide an effective absolute vector calibration standard at microwave frequencies.