Research On Microwave Photonic Phase Shift And Phase-coded Signal Generation Technology Based On Electro-optical External Modulation

As an indispensable key technology in radar systems,microwave photonic phase shift and phase-coded signal generation technology can flexibly control beam pointing,improve detection distance and distance resolution,and effectively solve the"electronic bottleneck"problem existing in traditional electronic technology.However,the existing photonic phase shift and phase-coded signal generation schemes have problems such as relatively single function and inability to realize wide-range frequency adjustment.It can't well meet the requirements of future radar systems of high frequency,large bandwidth,multi-function and low loss with the continuous development and use of high frequency electromagnetic spectrum.Therefore,this thesis mainly focuses on the photonic phase shift and phase-coded signal generation technology based on electro-optical external modulation.The specific work is as follows:(1)The research background of this thesis is introduced,and the advantages and main research directions of microwave photonic technology are summarized,and the research status of microwave photonic phase shift and phase-coded signal generation technology at home and abroad is summarized respectively.The basic structure and operating principle of several electro-optical external modulators are emphatically expounded,and some common sideband modulation methods based on MZM and DPMZM are deduced in detail.Finally,the radar pulse compression theory and phase-coded signal are summarized.(2)Aiming at the problem that the frequency multiplication factor in the existing microwave photonic phase shift schemes is relatively small and single,a multi-channel phase shift signal generation scheme with adjustable frequency multiplication factor based on PDM-DPMZM is proposed.In scheme,phase shift signals with frequency multiplication factor of 2,4,6,8,and 12 can be generated without filters,and the phase can be continuously linearly adjusted from 0 to 360°by simply adjusting polarizer.The generated adjustable frequency multiplier phase shift signals have flat phase response and power response,and have good frequency tunability.In addition,the operating frequency range covers 3.6?276 GHz,and the highest frequency is close to the terahertz band,which makes it have broad application prospects in high frequency and broadband radar systems.(3)In order to expand system functions,decrease system complexity and cost,and reduce the dependence on high frequency devices,a second harmonic mixing phase shift signal generation scheme is proposed.The proposed scheme can generate up/down converted and phase shift signals by changing the direct current bias voltage,and is suitable for both radar transmitters and receivers.This scheme only needs to adjust the polarization controller to generate mixed signals with a full range of linearly adjustable phase,and uses the local oscillator second harmonic component to participate in the mixing,reducing the requirements for the local oscillator signal frequency and the bandwidth of the modulator.The phase and power responses of the generated mixed and phase shift signals are flat at different frequencies,and the spurious free dynamic range is higher than 106.98 dB·Hz^2/3.(4)To improve the detection range and range resolution of the radar system,the improvement based on the phase shift scheme structures has been implemented.Moreover,there are two schemes for adjustable frequency multiplication factor phase-coded signal generation and dual-frequency phase-coded signal generation proposed.The two schemes do not use optical filters,and can generate phase-coded signals of any order with good frequency tunability.In the phase-coded signal generation scheme with adjustable frequency multiplication factor,the frequency multiplication factor can be adjusted between 2 and 12,which makes the system have the characteristics of large bandwidth.In the dual-frequency phase-coded signal generation scheme,balanced detection is adopted,which effectively eliminates the direct current component and other spurious signals,and improves the quality of the output signals.The scheme can be flexibly used in dual-band radar systems to improve the survivability,reduce the probability of false detection,and achieve functional diversification.Using 16-bit pseudo-random binary sequence for coding,performing Hilbert transform on the generated phase-coded signals,the recovered phase information is consistent with the original coding signal.The calculated pulse compression ratio after pulse compression is also close to the theoretical value of 16,indicating that the generated signals have good pulse compression performance.