4045

3823

كارشناسي ارشد

مخابرات

اصفهان: دانشگاه صنعتي اصفهان، دانشكده برق و كامپيوتر

1386

نه، [104]، [II] ص.: مصور، جدول، نمودار

ص. ع به: فارسي و انگليسي

محمود مدرس هاشمي

سعيد صدري

5/5/87

مهندسي برق و كامپيوتر

ID3823

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

AbstractNowadays radar systems play an important role in military and civil applications Among variousradar applications radar imaging constitutes an important one Imaging radars include bothSynthetic Aperture Radar SAR and Inverse Synthetic Aperture Radar ISAR In the SAR radar is usually carried by airplane or satellite and generates images from cities earth etc Onthe other hand in the ISAR radar is usually located in site and generates images from movingtargets such as missiles airplanes etc Conventional ISAR systems use Fourier Transform toretrieve Doppler spectrum and image formation But due to the complex motions of target theDoppler spectrum is time varying and hence the image formed by Fourier transform becomesblurred In such cases polar reformatting algorithm can be applied to compensate the effect oftime varying Doppler spectrum and prepare the results for the use of Fourier transform Unfortunately in situations where complex and maneuvering motions exist polar reformattingperformance is not acceptable In the 90s Joint Time Frequency Transforms JTFT has beenproposed to resolve the problems associated with Doppler spectrum and image formation In thisthesis the linear and bilinear JTFT including Cohen class transforms are reviewed Also TheFractional Fourier Transform FrFT is considered as a powerful tool for processing the signalswith time varying spectrum Finally FrFT and Smoothed Pseudo Wigner Ville Distribution SPWVD as a Cohen class transform are used for ISAR image formation The order of FrFTand the kernel parameters of SPWVD are adjusted by using Minimum Entropy criterion as localand total measures Statistical comparison of simulated FrFT based image with Fourier pdfMachine A pdf writer that produces quality PDF files with ease transform based and short time Fourier transform based images shows that FrFT is a proper toolfor ISAR image formation evenifat low SNR from a windows application documents Compatible across Produce quality PDF files in seconds and preserve the integrity of your original nearly all Windows platforms you can print you can use pdfMachine Get yours now

محمود مدرس هاشمي

سعيد صدري