Broadband Multiband Microwave Signal Up-conversion Technology Reseach

As a potential solution for solving congestion of signal traffic in low-frequency bands and achieving large-capacity and high-speed communication,signal up-conversion technology has great value in many fields such as optical communications,mobile communications,satellite communications and radar detection.For example,multi-band radar system has many advantages,such as multi-function detection,enhanced echo signal,improved immunity to interference,and the elimination of Doppler blind speed.As a key technique of multi-band radar system,multi-band signal up-conversion technology is getting more and more attention in recent years in radar system research.Utilizing electronic devices with limited bandwidth,multi-band radar system based on conventional electronic signal up-conversion technology would be built up by multiple set of separate hardware at different and discrete frequency bands,which would increase the complexity and cost of system.Owing to the ultra-wideband and reconfigurable characteristic of microwave photonic frequency up-conversion technology,a broadband and reconfigurable multi-band signal generator can be achieved.Hence,microwave photonic frequency up-conversion technology is a promising technique for high-performance and integrative system,such as modern communication system and radar system.This thesis focuses on multi-band microwave signal up-conversion technology to conduct theoretical simulation and experimental research.The main contents of this thesis can be summarized as follows:1.In order to solve the existing problem of mutual restriction of signal frequency range,number of frequency bands and power flatness which faced by current multi-band microwave generators,a multi-band microwave signal up-conversion technology scheme based on optical sampling is proposed.IF(intermediate frequency)signal is optically sampled by ultra-short optical pulse sequence via electro-optical modulation,as a result,the corresponding spectrum of IF signal is copied and moved to the discrete spectrum of the optical source.And then,the multi-band up-conversion processing of IF signal is realized by beating the different frequencies in broadband photodetector.Among them,the generation of ultra-short optical pulse is realized by the electro-optic modulation-based time lens and chirp compensation.In this thesis,simulation model of proposed system is established,and it is presented to obtain broadband and high-flatness multi-band microwave signal by optimizing the bias index and modulation index of intensity modulator in the ultra-short optical pulse source.Through numerical simulation,the ultra-short optical pulse source is optimized.Simulation results show that through optimizing the ultra-short pulse source with a repetition frequency of 8 GHz,ten phase-coded microwave signals are generated in the frequency range of 7 GHz to 41 GHz by employing a photodetector with a 3-d B bandwidth of 100 GHz,where the power flatness of the generated multi-band microwave signals is measured to below 3d B.The effect of matching dispersion on the power and flatness of multi-band microwave signal is analyzed and the spurious-free dynamic range(SFDR)of the system is evaluated.An ultra-short optical pulse source is experimentally built up.Researches on multi-band microwave signal generation system are carried out to realize a broadband and high-flatness multi-band microwave signal.And then,the feasibility of multi-band up-conversion and pulse compression of phase-coded signal was verified.Experimental results show that by optimizing the ultra-short pulse source and employing a photodetector with a 3-d B bandwidth of 40 GHz,ten phase-coded microwave signals with a 13-bit Barker code are generated in the frequency range of 7 GHz to 41 GHz,where the power flatness of the generated multi-band microwave signals is measured to be 5.9 d B.Meanwhile,the multi-band up-conversion of QPSK signal is achieved by changing the IF signal modulation format which proves the software-defined capability of the system.After frequency down-conversion,the error vector amplitude(EVM)value of the multiband QPSK signal is less than 2.05%.