Real-Time Measurement of Microwave Parameters and EM Fields

A technique for making fixed-frequency or wide-band real-time measurements of reflection coefficients, transmission coefficients, and fields in open or closed structures at UHF and microwave frequency is given. The basic system uses two isolated channels, which originate from a common CW source, and one channel is single-sideband modulated. These two signals are then added and mixed in a (homodyne) detector, and the detected signal at the modulation frequency displays the desired amplitude and phase information in real time simultaneously and independently. The sources of inherent phase and amplitude errors are considered, including those due to the unwanted sidebands created by imperfect modulation. Operation on the linear portion of the characteristic curve of a balanced detector tends to reduce these errors and increase the dynamic operating range. The system sensitivity should approach -110 to -120 dBm, and dynamic operating ranges of the order of 100 to 110 dB are possible.