Signal separation circuit for a radio frequency (RF) network analyzer

A signal separation circuit (108) for a radio frequency (RF) network analyzer includes a revering microwave switch for reversing signal flow to a device under test (DUT (111)) in a measurement of the S-parameters of the DUT (111). First and second reference paths are coupled to the signal paths beween the reverting switch and the DUT (111) connection ports for providing RF reference signals that are independent of switch repeatability and characteristics. The circuit includes a phase-locking frequency converter for converting the reference signals, and reflected and transmitted DUT response signals, to an intermediate frequency. The frequency converter is switchable to phase-lock either one of the reference signals to a reference oscillator signal. The circuit is usable with a precision vector network analyzer for laboratory and automated production measurements and had wide frequency capability from RF to millimeter bands.