The characteristic analysis and improvement based on group delay measurement of Frequency-Translating Devices by using double-frequency phase difference method

Double-frequency phase difference method is a simple and effective means for measuring the group delay of Frequency-Translating Devices (FTD). Especially for measuring the group delay of FTD which cannot accept the other local oscillator, the method shows the irreplaceable advantage. In order to obtain an accurate description of the group delay characteristics in the pass band of FTD, two improved methods are put forward in this paper which are variable aperture measurement method and multiple-frequency phase difference(MFPD) method on the basis of the measuring group delay by using double-frequency phase difference(DFPD) method. The variable aperture measurement method uses genetic algorithm (GA) to optimize the measurement aperture and the measurement interval on the basis of the rate of the group delay, and the measured data is handled with the cubic spline interpolation and Taylor series expansion method. Finally, an accurate group delay characteristics curve of the system is fitted. The MFPD method turns the double-frequency into the multiple-frequency on the basis of the DFPD method, which improves the testing efficiency and the measurement accuracy in a great extent. However, the premise is that the measured output spectrum should have enough signal-to-noise ratio. The simulation results show that these two improved methods are equally effective in reducing the measurement error and improving the measurement accuracy greatly.