Photonic Generation Of Wideband Chirped Microwave Signal And The Performance Analysis Of Pulse Compression

In modern radar systems,pulse compression technology is frequently applied to improve the radar detection capability.Generally,RF signal with a large time-bandwidth product is emitted at the transmitting end,then narrow pulses are obtained at the receiving end using matched filter.However,with the continuously arising demand,radar systems are moving towards ultra-wide operating frequency band and multi-functional integration.Traditional electronic radar systems are constrained by the limit of electronic devices,suffering from electronic bottlenecks such as limited bandwidth,poor tuning,and electromagnetic interference.Moreover,it is difficult to generate signals with large time-bandwidth product.In recent years,the emerging microwave photonics,which combines microwave technology with optics,features the advantages of high frequency band,large bandwidth,low power consumption and small size,and is free from electromagnetic sensation,thus has received extensive attention and research.In view of the above issues,this thesis focuses on the photonic generation of linear frequency modulation(LMF)signals,and provides theoretical analysis,mathematical derivation and simulation results.The detailed research contents are shown as follows:1.Microwave photonics and modern radar systems are introduced,including the current status and progress of microwave photonic radar and LFM signal generation technology.In particular,the pulse compression technology and optical external modulation technology are analyzed in detail.2.Three existing typical schemes for LFM signal generation are theoretically analyzed and simulated,including the generation scheme based on optical pulse spectrum shaping and frequency-time mapping,the scheme based on optical microwave frequency multiplication,and the scheme based on cascaded Mach-Zehnder modulator(MZM).Furthermore,characteristics and deficiencies of those three schemes are compared and summarized.3.A novel LFM signal generation scheme,which is based on dual-parallel quadrature phase shift keying(DP-QPSK)modulator and phase modulator,is proposed.Based on the principle of continuous optical signal external optical phase modulation,the proposed scheme using an integrated modulation device avoids the influence of tuning with filter in other schemes on system performance.LFM signals with center frequency of 10 GHz(or 20 GHz)and bandwidth of 2 GHz(or 4 GHz)are generated in the related simulation.The results show that tuning performance of the proposed scheme is preferable.4.Furthermore,a novel double-frequency dual-chirp LFM signal generation scheme,which is based on dual-parallel MZM(DP-MZM),is proposed.In this proposed scheme,the dualchirp signal is generated using only one modulator,which can effectively avoid the influence of the range-Doppler coupling effect on the radar system's detection precision.The frequency doubling function reduces the demand of a high-frequency local oscillator,allowing the generation of higher-center-frequency LFM signals.Dual-chirp LFM signals with highest center frequency of 20 GHz,bandwidth of 4 GHz,and duration of 1?s are successfully generated in the related simulation.The related results show that the pulse compression ratio reaches 3704,which implies excellent pulse compression performance.