On The Improvement Of Inverse Synthetic Aperture Radar (ISAR) Imaging Techniques

ANSmCTInverse Synthetic APerture sadar (ISAR), in which the radar isstationary and the target is moving, can work a1l day, al1 weather andhas become one of the nain techniqUes in imaging the moving target farfrom the sensor. More and more research on ISAR has been carried outbecause of 1ts potentia1 app1ications in civi1 and mi1itary app1ications.A1most of a11, the conventional ISAR research 1s based on the scatteringmode1, that is, the scattering prOPerty of the target ca-n be modeled tyan asseInbly scatterers and the thege of the target can be achieved tysimple Range--DoPP1er a1gorithIn (RDA). Because of the non--cooperativityof the target and the cOmp1exity of the movenent, the ISAR techniqUes,inc1uding the ra-nge alignInent and theging a1goritbo, can not a1waysresult in satisfactory resu1t in rea1 data processing. The main work ofthis dissertation focuses on two aspects. The first,, the existingprob1ems, such as range a1irment and scatterer Migration ThroughResolution Cell (mRC), in real data processing, are discussed and thecorresponding a1gorithins are proposed to deal with the problems; Second,the real time imaging for maneuvering targets is carried out and a simp1eRange--Instantaneous DoPPler (RID) a1gorithIn is deve1oped. The detai1sof the dissertation is as fo1low:In ISAn imaging, data--driven coInPensation of motion is necessarybecause of the difficu1ty in measuring the motion paraneters of thenon--cooperative targets, where the range a1impent is one of the key steps.The conventional range a1ipent method, i. e., the enve1ope corre1ationmethod, often brings inaccurate aligrment resulting from drift errorsand jmp errors. To remove the errors, the non--paraneter minina entroPy(ME) method was proposed. As indicated in a 1ot of results of real data,ME method can guarantee the g1oba1 range alignent. In ChaPter 2, thetheoretica1 analysis of ME method is presented. The iraging resu1ts ofreal data verify the correctness of the ana1ysis and the effectivenessof the ME method.Because conventiona1 range a1igrment methods asscoe that scatterers'positions are a1most fixed during the iareging interval, which reqUiredthe target be rigid, it is not easy for us to obtain good resu1t for thetarget with moving P8rts (such as the prOPe1lers on An-26 aircraft) usingthe conventiona1 bethod. In Chapter 3, the effects of the prOPel1ers sub-echoes on the return and the rope alimpnt are ana1yzed using the rea1data of An-26 aircraft. A modified method for this specia1 case isproposed, in which several returns with sca11er dynanic range areselected first tc generate the reference echo, and then the effect ofthe prope1lers on the returns with 1arger dynanic range is weakenedthrough the adaptive thresho1ding. The fina1 results of the rea1 dataconfirn the rodified range alignInent method.After the motion cOmpensation, the image of the target can be obtainedby tuge-DoPP1er method. To obtain radar thege of a target, certain op1eof the target with respect to Radar Light Of Sight (RLOS) during thecoherent integration interva1 is reguired, that is, the motion is thesource of ISAR icagieq. however, it is also the source of problem (suchas rv). Actua11y, scatterers' rm hapPens inevitab1y in higherreso1ution radar image,which wi11 resu1t in the POint--spread functionbroadeninq and image reso1ution decreasing. In ChaPter 4, the scatterers'migration in ISAR is analyzed and the 2--D space--variant comPensation isreduced Lo two l--D coInPensations. And a siInP1e and efficient method isproposed to cOInPensate MTR - In the proposed wrRC COInPensation AlgorithIn,scatterer migration range resolution ce1l can be cOInPensated withoutthe know1edge of rotating parameters. CoInPensation resu1ts of thesiamlated data and the rea1 data co11ected in a microwave anechoic chaInbershow that the reso1ution of the fina1 radar theges is twroved.The re1ationship between rv CoInPensation a1gorittri...