New methods for testing frequency converters with embedded local oscillators

Previous methods for characterizing the magnitude, phase and group delay responses of a mixer required access to the LO. In satellite systems the LO may be internal to the frequency converter and not accessible, nor perfectly stable. Here, a method is developed that can measure the response of a mixer with an embedded LO. This method works by phase tracking the IF of the converter output and using that information to determine the frequency and phase drift of the embedded LO, and compensate for any drift. The accuracy of the response is limited by the phase-noise quality of the internal LO, and methods are described for compensation of this noise. This method can provide the absolute group delay response, and on a typical Ka band satellite converter, delay accuracy as small as 125 ps have been achieved.