Research On Microwave Photonic Ranging Technology

As critical equipments for navy,air force,land force and space force,radars play an important role in modern military warfare,which undertakes the mission of monitoring and tracking military targets in complex environments and harsh climates.Traditional radars based on electronic technology are difficult to generate and process broadband signals due to the well-known electronic bottleneck,which puts a limit on the range resolution.Microwave photonic technology has prominent advantages such as ultra wideband,low transmission loss and immunity to electromagnetic interference.Hence,it is a promising candidate to break the electronic bottleneck and improve the radar detection performance.This thesis focuses on the radar ranging detection system based on microwave photonic technology.A novel approach to generating Costas-coded frequency hopping linear frequency modulation(LFM)signal is proposed based on a Fourier-domain mode locking(FDML)optoelectronic oscillator(OEO).By using the generated Costas-coded frequency hopping LFM signal,radar ranging detection is experimentally demonstrated.The main contents of this thesis are summarized as follows.(1)The development history and the research status of radar ranging detection based on microwave photonic technology are analyzed.In addition,the operation principle of radar ranging detection is studied,where special attention is paid to the influence of the fuzzy function on the ranging detection performance.Numerical simulation is carried out to evaluate the fuzzy function and the ranging detection performance of various signal waveforms including LFM signal,phase-coded signal,Costas-coded frequency hopping signal and Costas-coded frequency hopping LFM signal.Results indicate that the Costascoded frequency hopping LFM signal has an ideal fuzzy function and low sidelobes after pulse compression.Hence,it is favorable for eliminating the distance-Doppler coupling in detecting a moving target.(2)An approach to generating Costas-coded frequency hopping LFM signals with low phase noise and large time-bandwidth products is proposed and experimentally demonstrated based on a FDML OEO driven by a voltage-controlled oscillator(VCO).In this approach,a fast-scanning microwave photonic passband filter(MPF)is used to select the oscillation modes and maintain FDML status in the OEO cavity.The fast-scanning MPF is realized by using a frequency-scanned probe light generated via an open-loop VCO-controlled electro-optic frequency shift to achieve frequency-selective phasemodualtion-to-intensity-modulation conversion via simulated Brillouin scattering effect.In the experiment,bandwidth and frequency reconfigurable Costas-coded frequency hopping LFM signals with a 12-bit Costas code sequence are generated.The crosscorrelation results indicate that the generated signals have excellent coherence.(3)Radar ranging detetion is experimentally demonstrated based on the generated Costas-coded frequency hopping LFM signal.In the experiment,two short-range objects separated by 0.2 m,0.3 m,0.5 m,0.85 m and 1 m are successfully distinguished by using pulse compression method and dechirp method,respectively.In addition,an optical fiber with a length of 50 km is used to emulate the long-range target,where the experimental results indicate that the excerllent coherence of the Costas-coded frequency hopping LFM signals generated by the FMDL OEO is beneficial for improving the radar ranging detection performance.