How to Measure RF Phase Noise

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Optimizing RF phase noise through advanced measurement methods

Measuring phase noise is essential to optimizing narrow channel communications in RF transmissions. The instability of the oscillator causes phase noise, which appears as jitter in the time domain. Phase noise impacts the signal quality and increases error rates in communications links. Unlike other signal noise, phase noise is best understood in the spectral domain.

There are three common techniques for measuring phase noise: direct spectrum, phase detector, and two-channel cross-correlation. The direct spectrum technique measures the spectral energy of the broadband signal using an instrument like a spectrum / signal analyzer, but there are limitations due to the amplitude noise mimicking phase noise. Advanced applications use a dedicated phase noise instrument that employs a phase detector and two-channel cross-correlation techniques. Both techniques operate on the baseband signal and require a downconverter.

RF phase noise measurement solution

RF phase noise measurement solution

Measuring RF and microwave frequency phase noise requires a dedicated phase noise instrument. The Keysight RF phase noise measurement solution uses the Keysight N5511A phase noise test system, the Keysight E5055A SSA-X signal source and the Keysight E5053A microwave downconverter to deliver accurate phase noise measurements with an ultra-low noise floor. Both absolute and residual phase noise can be measured down to kT (-177 dBm/Hz).

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