Resolution Analysis Of GNSS Passive Imaging Radar Based On Generalized Ambiguity Function

Passive imaging system is a kind of passive bistatic SAR/ISAR system,which uses the non-cooperative illuminators as the transmitters.The direct signals from non-cooperative illuminators and the reflected signals from targets are received by the receivers and are used to detect or image the targets in passive imaging system.Due to its prominent advantages in comparison to active radars,such as low probability of interception and flexible configuration,passive imaging system has drawn a lot of attention all over the world in recent years.There are many advantages of global navigation system,such as a large number of navigation satellites,global coverage and short revisit cycles,which make it perfect for being used as the illuminators for passive imaging system.The spatial resolution is one key factor of the performance for SAR/ISAR systems.This article researches on the ambiguity function of the passive imaging system based on GNSS signals and analyzes the resolution capability of passive system.A scheme based on position adjustment of receiving station is derived and the comprehensive utilization of various navigation systems is studied.According to the characteristic of GNSS signals,the concept of average ambiguity function is introduced to remove the effect of particular pseudo-random code on resolution capability and the formula of the generalized ambiguity function of passive imaging system based on GNSS signal is derived.Linear incoherent processing and linear coherent processing are used to analyze the resolution capability of multi-static passive imaging system.The results show that the new generalized ambiguity function can be used to study the resolution capability of passive system based on GNSS signals more reasonably.The position adjustment of receiving station is the only way to improve the resolution capability.According to the relationship between resolution and support region in wave-number domain and the relationship between resolution and ambiguity function,some guideline for optimization of cconfiguration of receiver station is summarized in this article.The results indicate that the impact of receiver's location on the resolution capability of passive imaging system based on GNSS signals can be almost ignored.Finally,the influence of different kinds of GNSS signals on the resolution performance of passive system is analyzed and the comprehensive utilization of various navigation systems is studied.It can be concluded from the simulation results that when the bandwidth of the selected GNSS signals becomes bigger,the resolution capability of imaging system is better and the influence of receiver's location on the resolution becomes more obvious.