Research On Technologies Of Photonics-based Radar Signal Generation And Measurement

Radar has been widely used in military and civilian fields,due to the excellent perception ability.Modern radars need to use multi-formats,larger-bandwidth radar waveforms,and apply more sophisticated measurement techniques,to meet the increasingly complex detection environment and achieve higher-resolution detection tasks.However,the above-mentioned requirements make traditional electronics suffer from the double dilemma of exponentially increasing system complexity and limited device bandwidth.In this context,the use of microwave photonic technology with the advantages of small size,low loss,and large bandwidth to generate and process radar waveforms is of great academic as well as application value.In this dissertation,technologies of radar signal generation and measurement based on photonics are mainly studied.Several photonic schemes have been proposed to solve the problems of limited signal bandwidth,insufficient measurement accuracy,and higher system complexity in traditional electrical or existing photonic schemes.For example,schemes to generate signals including dual-chirp waveform,multi-format chirp waveform,joint radar and communication waveform,have been proposed and experimentally demonstrated.They can satisfy the waveform requirements for different radar systems such as pulse compression radar,multifunction radar and intelligent radar.Besides,two schemes with high precision,large bandwidth and no directional ambiguity have been proposed to measure the Doppler frequency shifts for the first time,of which the implementations are based on I/Q detection and introducing a reference signal,respectively.The major contributions and innovations of this dissertation are as follows.(1)A photonic approach for dual-chirp waveform generation is proposed based on a single DPMZM,which can solve the range-Doppler coupling effect.The bandwidth of the output dual-chirp waveform is doubled,compared with that of the input single-chirp signal.Anti-chromatic dispersion transmission of dual-chirp waveform is investigated.Theoretical derivation,simulations and experiments results demonstrate the feasibility of working in back-to-back and distributed conditions.The integrated modulator and external modulation technology ensure that the system has a compact structure,stable operation,and flexible adjustment.(2)A novel photonic multi-format chirp waveform generation scheme is proposed and demonstrated by both experiments and simulations.Anti-dispersive power fading technology in multi-format signal generation and switching is investigate for the first time.Theoretical derivation and experimental verification under multi-format signals and multi-working scenarios enrich the universality of the system.The generation of frequency-multiplied signals allows the system to have a smaller measurement resolution.The simplification of the applied modulator and the avoidance of broadband phase shifters reduce the bandwidth constraints,thus increasing the feasibility of the system.(3)A synthesizer for joint radar and communication waveform is investigated based on continuous photonic time compression.This provides a new idea for joint radar and communication waveform generation with high carrier frequency,large bandwidth,and high speed,thanks to the signal compression and time division multiplexing.An improved scheme based on single-sideband modulation can solve the serious power fading problem that exists in the synthesizer.The theoretical model of the system is deduced in detail.The experimental and simulation results are consistent with the theoretical deduction.(4)Regarding the Doppler frequency shift measurement,a photonic Doppler frequency shift measurement scheme by introducing a reference signal is proposed,which can realize high-precision,large-bandwidth Doppler frequency shift measurement.The principle of I/Q detection further improves the measurement accuracy.In the above schemes,the phase modulator is connected in parallel with an acousto-optic modulator or cascaded with the dispersive medium.Using a phase modulator instead of an intensity modulator makes the system simple and stable,avoiding measurement errors caused by bias drift.Measurements with large bandwidth and high precision can be achieved,and excellent performance is also presented.In conclusion,this dissertation focuses on the research of radar signal generation and measurement technology based on photonics.Our research explores the potential development direction of microwave photonic radar technology.It provides new technical accumulation for the application of photonic technology in radar system.