Study On Passive Synthetic Aperture Radar Imaging Methods

Synthetic Aperture Radar achieves high range resolution upon transmitting signals with largeTime-Bandwidth-Product (TBP) and achieves high azimuth resolution by the large synthetic antennaaperture which is formed by the movement of radar platform. Due to its all weather, day and nightcapability, SAR has been proven to be a significant technology in military and civil applications.Passive radar does not transmit signal itself, but manages to locate and image by receiving thesignals reflected by targets from other illuminators. Due to its good performance in electromagneticcountermeasure and its capability to solve the band crowd problem in urban areas, passive radar usingilluminators of opportunity becomes an active research area in recent years. With the rapid growth inthe number of civil sources of opportunity in urban areas, such as FM radio stations and TVbroadcasting stations, mobile phone base stations, etc, there’s no doubt that passive radar usingilluminators of opportunity will get better development in the coming future. Considering that theexisting passive imaging systems usually require a priori information of the transmitters’ location andthe transmitting waveforms, as well as the requirement of antenna with high directivity, thecomplexity of radar system is increasing accordingly with all the requirements. Consequently, it haspractical significance to study on passive imaging method without the priori information of thetransmitters.Taking advantage of the traditional SAR’s high resolution by forming a large synthetic aperturefrom the movement of receiver platform, C. J. Nolan has taken a successful implementation towardsimaging of two-dimensional targets on the ground based on mono-SAR hitchhiker. Consideringvarious advantages of the method, the dissertation discusses the passive SAR imaging method inbistatic/multiple cases to make it applicable to one/multiple airborne receivers and one/multiple,static/mobile, cooperative/non-cooperative illuminators of opportunity. This dissertation provides anovel method for passive radar imaging using illuminators of opportunity. It will start with thespatio-temporal correlation when the location and the signal waveform of the transmitters is unknown,then use the FBP technology to reconstruct the scene radiation of the ground target, which may breaka new path to the passive radar imaging based on the sources of opportunity.Chapter I is the introduction, which introduces the background of this paper and describes thehistory and the latest developments in passive SAR and passive imaging methods. Based on the waveequation and Born approximation, this chapter briefly introduces the data model of received signalfrom mono-SAR and gives a deduction of the FBP inversion signal processing. At last, the difficultiesand main contents in research are outlined. In Chapter II, the implementation of passive SAR imaging algorithm using ultra-narrowbandContinuous Wave (CW) waveforms is proposed. This chapter presents a novel image formation methodfor passive SAR using narrowband or ultra-narrowband CW waveforms. First, the data model is builtup for imaging by correlating the signals received from different airborne receivers, and the correlationmodel is discussed under cooperate situation and non-cooperate situation respectively. Then we analyzethe essence of the imaging method by defining two types of contours, iso-Doppler contours andiso-Doppler-rate contours. Finally, various potential factors that influence the quality of the imaging areanalyzed by the introduction of data collection manifold.In Chapter III, the implementation of passive SAR imaging algorithm using traditional largebandwidth waveforms is proposed. First, we discuss the correlation model of the received signals undercooperate situation and non-cooperate situation respectively. Then we analyze the essence of theimaging method by defining two types of contours, iso-Range contours and iso-Doppler contours, andanalyze various potential factors that influence the quality of the imaging by introducing of datacollection manifold. Finally, the procedures and computational complexity of the passive SAR imagingare given.Chapter IV studies several signals of civil illumintors of opportunity, which are now widelydistributed in urban areas, such as Frequency Modulated (FM) Radio Broadcasting signals, andDigital Video Broadcasting signals (DVB) and signals of Worldwide Interoperability for MicrowaveAccess (WiMAX). This chapter discusses the mentioned signals by analyzing their signal structureand ambiguity function respectively.In Chapter V, numerical simulations demonstrate the performance of the echo-correlation andFBP based passive SAR imaging method and verify theoretical analysis of main factors that influencethe quality of the reconstructed image. Then we discuss the correlated K distributed sea clutter model,and use the simulations of the scene with clutter to demonstrate the effectiveness of the method at last.