Research On Coherence Of Passive Radar Base On Space-Based Signal

Passive Radar base on Space-based signal is a dual-base radar that uses satellite signals as external radiation sources.The radar itself does not have a transmitter,but detects and locates and tracks the target by receiving the reflected wave from the target to the satellite signal.Its battlefield survival and anti-stealth ability are strong,and its application prospects on the future battlefield are broad.Among them,when medium-high orbit satellites,especially high-orbit navigation satellites,are used as external radiation sources,since the signal itself is very weak,and the high orbit has a longer range,the target's reflected wave to the satellite signal is weaker,and it needs to be extended.Time is accumulated to increase the target energy in the echo signal,otherwise it will not be able to effectively detect,locate and track the target.In response to this problem,this thesis focuses on several factors and models that affect the coherence of space-based external radiators.The main work is as follows:First of all,a target echo signal model based on the transmission signal of the medium and high orbit satellites and the receiving configuration of the ground-based,airborne and low-orbit satellites is established.Based on the ambiguity function theory,the ambiguity of the distance and speed of the three satellite signals of DVB-S,ABS-S and GPS is analyzed.Using these three satellite signals as external radiators,the basic performance of external radiator radars,such as target echo signal-to-noise ratio,direct wave power,and maximum detectable target distance,are analyzed.Then,the evaluation index of the echo signal coherence performance is established,focusing on the analysis of phase noise,phase advance and Faraday rotation caused by the ionosphere,parameter estimation error,and the basic theory and mathematical model of decoherence for multipath effects.Among them,the position of the puncture point where the signal passes through the ionosphere will change with time when receiving low-orbit satellites.This thesis establishes a model of the ionospheric puncture point change,and analyzes the influence of the puncture point change on the coherence of the external radiator radar echo signal.Finally,the effects of phase noise,ionospheric decoherence,parameter estimation errorsand multipath effects on long-term coherent accumulation are discussed.Through simulation analysis,it is concluded that random phase noise will bring a certain coherent accumulation loss.As the accumulation time increases,the accumulation loss will gradually decrease and approach a fixed value;the coherent accumulation time exceeds the decoherence time of the ionosphere When the accumulation time is five times longer,the coherent accumulation effect is hardly improved;the parameter estimation error causes the coherent accumulation performance to gradually decrease after reaching a peak,which will limit the performance of the coherent accumulation;in the presence of multipath effects When performing coherent accumulation,the energy of some non-interested targets will also increase,causing a certain accumulation loss.