Research On Photonic Generation Of Phase-Coded Microwave Signal And Doppler Frequency Shift Measurement

Photonic generation of phase-coded microwave waveforms and measurement of the Doppler frequency shift are essential technologies in modern radar system.As the increase of the frequency band,the radar system is developing towards ultra-wide operating frequency band,re-configurability and multifunction.Traditional electrical technologies in signal generation and frequency measurement cannot meet the requirements in the future radar system since they suffer from the bottleneck including limited bandwidth,inflexible frequency tunability and electromagnetic interference?EMI?.Photonic generation of phase-coded microwave signal features high carrier frequency,tunable band and larger time-bandwidth product.Photonic measurement of the Doppler frequency shift has the advantages of wide carrier frequency range and tiny measurement error.Both of the two technologies are immune to the EMI and thus have been intensively researched.However,the reported photonic methods of phase-coded signal generation exhibit a low frequency multiplication factor and have strict requirements on the LO signal.The measurement systems of the Doppler frequency shift are always bulky and hard to implement.To solve these problems,theoretical analysis,simulations and experiments are carried out for photonic generation of phase-coded signal and measurement of the Doppler frequency shift in this thesis.The detailed contents are as follow:1.A photonic approach to generate a phase-coded microwave waveform based on a dual-parallel quadrature phase shift keying modulator?DP-QPSK?is theoretically proposed and studied by a simulation.Compared with other methods,only an external modulator is used and no any filter is needed in our approach,which makes the system stable and tunable.2.A photonic approach to generate a phase-coded microwave waveform with frequency quadrupling based on a dual-parallel Mach-Zehnder modulator?DP-MZM?is proposed and experimentally demonstrated.The approach can reduce the requirement of the LO signal effectively and the signal modulated by arbitrary waveform can be obtained.In the experiment,the 12-GHz and 24-GHz waveforms modulated by binary and quaternary code patterns are demonstrated.The compression capacity is also studied and the results accord well with theoretical analysis.3.A photonic approach to generate a phase-coded microwave waveform based on a mode locked laser?MLL?with arbitrary frequency multiplication factor is theoretically proposed and studied by a simulation.This system further reduce the requirement of the LO signal and the phased coded signals with higher carrier frequency can be obtained.4.A photonic approach to measure the Doppler frequency shift based on a single DP-MZM is proposed and experimentally demonstrated.The echo signal is down-converted by the LO signal.The absolute value of the Doppler frequency shift can be measured by the low-frequency signal and the sign can be obtained based on the phase difference of the upper and lower sidebands.The system is compact and easy to implement.A wide carrier frequency range from 10GHz to 39GHz is achieved with measurement errors within?5?10^-6Hz.