Many RF systems require very tight frequency and/or timing control, particularly as one goes above C or X band, or if strict limits on phase errors are specified.  Usual applications include deep space Doppler and ranging, radar, digital broadcast, cellular communications, positioning, GNSS disciplined low-phase noise oscillators, etc.   In addition to radios and transponders that rely on precise time transfer, we have developed test instruments for quantifying the phase precision and thermal stability of systems that operate at X-band and beyond.