Synchronization of a millimeter-wave BWO with a spectrum analyzer via a simple phaselock system

The evaluation of very low loss materials in the millimeter-wave region requires precision measurement of the change in the linewidth of a resonant cavity when a sample is inserted. The precision required is on the order of a few kHz change in a 300 kHz linewidth. For a number of years we have utilized the combination of a backward wave oscillator (BWO) source and a microwave spectrum analyzer to obtain such measurements.