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Enhancing the frequency stability of a millimeter wave network analyzer with an add-on unit

A proper arrangement frequency generation greatly enhances the stability of commercial millimeter wave instrumentation, particularly in network analyzers operating above 110 GHz. When distributed crystal clocks of varying uncertainty classes are replaced by a centralized rubidium master oscillator, the phase and frequency errors of the entire measuring system are reduced by a factor of ten. Galvanic ground loops and load pulling effects can be entirely avoided in these physically large installations by using optical fibers as a synchronization path. Millimeter wave spectrum characteristics remain unaffected because no additional phase locked loops or frequency multipliers are needed. The suggested modification is of great help in prolonged near-field scanning measurements, where a constant phase and carrier frequency have to be maintained even for a couple of days. Repeatability is extended up to several months through GPS-based frequency steering, which however must be disabled during millimeter wave activity in order to avoid phase jumps.