Phase Noise Measurement

Phase Noise is a basic property in VCO design. Measuring Phase Noise requires a carefull treatment.
One way of is to measure phase noise directly on a spectrum analyzer. This measurement can be done as long as the analyzer has better phase noise than the measured source.
VCO phase noise can be measure when the VCO is locked in the PLL loop or in open loop.
The first method is easier to measure but then you see phase noise of both VCO and the loop.
The second method gives directly the VCO noise, but you have to hold Vtune with a very clean source.