Measurement Of Group Delay Based On Frequency Modulated Signal

With the development of electrical systems,people pay more attention to the phase frequency characteristics of the transmission network which determine the distortion of the signal during transmission that named group delay.The performance of positioning navigation systems and communication systems is directly affected by the measurement accuracy of the group delay.Therefore,the group delay measurement technology has become one of the most popular research subjects in many fields.Among the many group delay measurement methods,the measurement method based on the vector network analyzer(VNA)is complicated and requires an analog closed-loop system.For the group delay characteristics of frequency converter devices,an additional reference signal is required,which cannot be directly measured.For the existing group delay dynamic measurement methods,the system structure is complicated,and the modulation as well as demodulation devices used will additionally introduce electrical noise,resulting in low system measurement accuracy.In this dissertation,the group delay measurement method based on frequency modulation signals is studied in depth,and a new group delay measurement method is proposed.Firstly the research background and application of RF delay measurement technology is introduced.The existing group delay methods are theoretically analyzed,whose advantages and disadvantages are summarized.The principle of multi-tone signal measurement method is deduced,and the efficiency and accuracy of delay measurement are analyzed.Then error has been analyzed through MATLAB calculation.Secondly,the frequency leakage phenomenon in the discrete Fourier transform(DFT)is used to explain the errors in the group delay measurement based on the multi-tone signal,and then the cause of the spectrum leakage is analyzed.The theoretical derivation of the all-phase DFT is performed and the characteristics of the all-phase DFT are analyzed.In addition,the all-phase DFT is used in the group delay measurement system based on multi-tone signals.At the same time,the measurement results are simulated on MATLAB.The actual measurement effect of this method in group delay is verified by setting up an experimental system to measure the linear phase system,the nonlinear phase system and frequency conversion system separately.The phase ambiguity phenomenon in the measurement is analyzed.To mitigate fuzzification,the improved Chinese remainder theorem(CRT)is adopted.Aiming at the problem that the resolution and measurement accuracy are inconsistent by using traditional phase differential method,a group delay measurement method based on orthogonal demodulation of chirp signal is proposed and the principle of group delay measurement is derived.The detailed analysis is made on the factors which affect the measurement accuracy of the system.In the study,the simulation using MATLAB tools is performed,and the system simulation results under different parameters are provided.The experimental results show that this method is suitable for group delay measurement with different apertures and different ranges.Compared with the conventional group delay dynamic measurement methods,it has more advantages in small aperture measurement and should be more effective in group delay measurement with small aperture compared with the group delay detection method in transmission.