Application of Phase Discriminator Error Model to Pulsed RF Measurement System Calibration

Abstract

A method is presented for applying direct detection (no local oscilator) I/Q detectors (discriminators) to obtain accurate phase and gain measurements without continuously leveling the sampled signals. The method applies the phase discriminator error model described in an eariler paper ("Coherent I/Q Detector Performance Under Extended Drive Signal Conditions", 27th IEEE ARFTG, June, 1985) in such a way as to account for discriminator and system signal sampling channel phase and attenuation imbalance. The calibration results refer I & Q measurements directly to the device under test (DUT) input and output ports. The method accounts for discrimiator error as a function of device gain. The calibrated system is effective over 18 dB of dynamnic device gain with no phase ambiguity. Phase and gain accuracy is better than 1 degree and .1 dB respectively. For calibration reference, the system utilizes two standard step attenuators and a bi-phase modulator precalibrated on an Automatic Network Analyzer under continuous wave conditions. These devices provide known gain and phase conditions referenced to the DUT ports. The method and hardware yield a simple and cost effective way to generate accurate, repeatable pulsed RF phase and gain measurements.