Phase Noise Measurement System Based On Frequency Discriminator

Phase noise refers to the random variation of the phase of the frequency source's output signal which is under the influence of internal various active devices.It is one of the important indicators to measure the frequency stability of frequency source.With the development of electronic technique and the emergence of high-performance microwave oscillator,the commercial phase noise measuring equipment has not met the current demand,another method to measure lower phase noise are needed.The frequency discriminator method for phase noise measurement is a measurement method with high accuracy and relatively simple system structure.However,the traditional frequency discriminator method is only feasible in theory,which is difficult to be applied in practice due to its excessive power loss.With the development of optoelectronic technology,the frequency discriminator method based on optical fiber delay line has been widely used.The advantage that it can be measured without reference source makes it to be one of the methods to measure phase noise with high-performance frequency source.Firstly,this thesis introduces the measurement principles of various commonly used measurement methods for phase noise,and then carries out in-depth research on the frequency discriminator method.For the widely used optical fiber delay self-heterodyne method,this thesis improves it and designs a complete phase noise measurement system.Finally,different power spectral density estimation methods for the results of phase noise measurement are discussed.According to the estimation results,their estimated performances are compared to find an estimation method suitable for phase noise measurement.The main work and contribution of this thesis are as follows:1.An improved phase noise measurement system based on frequency discriminator is proposed,in which the phase shifter is replaced by a tunable optical fiber delay line.Therefore,the insertion loss is not changed when the phase is adjusted.Consequently,the power of the local oscillator is stabilized,and the strict linear relationship between the RF ends and IF ends of the mixer is maintained.2.The phase noise measurement system proposed in this thesis is demonstrated and it can completely realize the function of phase noise measurement by circuit design,program design and system construction.3.The estimation principles and estimation performances of several estimation methods are investigated and compared.By estimating the same original data of phase noise measurement using different estimation methods,a relatively suitable estimation method for phase noise measurement is found.