Tesi di dottorato di ricerca
Innovative SAR & ISAR Signal Processing
Settore scientifico disciplinare
Corso di studi
tutor Berizzi, Fabrizio
- signal processing
Data inizio appello
This thesis reports on research into the eld of Synthetic Aperture Radar<br>(SAR) and Inverse Synthetic Aperture Radar (ISAR) signal processing. The<br>contributions of this thesis may be divided into two following parts:<br> A new bistatic 3D near eld circular SAR imaging algorithm was devel-<br>oped. High resolution radar imaging is typically obtained by combining<br>wide bandwidth signals and synthetic aperture processing. High range<br>resolution is obtained by using modulated signals whereas high cross<br>range resolution is achieved by coherently processing the target echoes<br>at dierent aspect angles of the target. Anyway, theoretical results have<br>shown that when the aspect angle whereby the target is observed is suf-<br>ciently wide, high resolution target images can be obtained by using<br>continuous wave (CW) radars , therefore allowing to reduce hardware<br>costs. In a similar way, three dimensional radar imaging can be per-<br>formed by coherently processing the backscattered eld as a function of<br>two rotation angles about two orthogonal axes .Three dimensional tar-<br>get radar imaging can be eciently obtained by means of a 3D Fourier<br>Transform, when the far-eld (planar wave) approximation holds. Oth-<br>erwise, the wavefront curvature has to be accounted for. For this reason,<br>a new algorithm based on a near eld spherical wave illumination that<br>takes into account the wavefront curvature by adopting a planar piece-<br>wise approximation was designed. This means that the wavefront is as-<br>sumed to be locally planar around a given point on the target. The oper-<br>ator that the algorithm uses for the focusing procedure is a space variant<br>focusing function which aims at compensating the propagation losses and<br>the wavefront curvature. The algorithm has been developed under the<br>Microwave Electronic Imaging Security and Safety Access (MELISSA)<br>project. The system MELISSA is a body scanner whose purpose is the<br>detection of concealed objects. The added value of the system is the<br>capability to provide an electromagnetic image of the concealed objects.<br>The author would like to thank all people that worked at the project, all<br>LabRass colleagues, all people who designed and acquired real data, all people that permitted the drafting of the rst part of this thesis. The<br>developed algorithm was presented in the chapter 1. The goal of this<br>work was the system design concerning the imaging point of view, by<br>simulating and therefore predicting the system performance by means of<br>the developed algorithm. In the chapter 2 was shown how the design was<br>achieved. Finally, in the chapter 3, the results on real data measured in<br>anechoic chamber with a system with characteristics very close to the<br>nal system prototype MELISSA, was presented.<br> A new way of ISAR processing has been dened, by applying the tradi-<br>tional ISAR processing to data acquired from passive radars. Purpose of<br>the ISAR processing is to extract an electromagnetic bi-dimensional im-<br>age of the target in order to determine the main geometric features of the<br>target, allowing (when possible) recognition and classication. Passive<br>radars are able to detect and track targets by exploiting illuminators of<br>opportunity (IOs). In this work of thesis, it will be proven that the same<br>concept can be extended to allow for Passive Inverse Synthetic Aperture<br>Radar (P-ISAR) imaging. A suitable signal processing is detailed that<br>is able to form P-ISAR images starting from range-Doppler maps, which<br>represent the output of a passive radar signal processing. Multiple chan-<br>nels Digital Video Broadcasting - Terrestrial (DVB-T) signals are used to<br>demonstrate the concept as they provide enough range resolution to form<br>meaningful ISAR images. The problem of grating lobes, generated by<br>DVB-T signal, is also addressed and solved by proposing an innovative<br>P-ISAR technique. The second part of this thesis has been developed un-<br>der the Array Passive ISAR adaptive processing (APIS) project. APIS is<br>dened as a multichannel, bi-static single receiver for array passive radar,<br>capable of detecting targets and generating ISAR images of the detected<br>targets for classication purposes. The author would like to thank all<br>people that worked at the project, all LabRass colleagues, all people who<br>designed, built the prototype and acquired real data, all people that per-<br>mitted the drafting of the second part of this thesis. In the chapter 4, the<br>basics on Passive Bistatic Radar (PBR) was brie<br>y recalled, the P-ISAR<br>processor was detailed and the new algorithm per the Grating Lobes<br>Cancellation was presented. In the chapter 5, some numerical results<br>on simulated data was shown, in order to demonstrate the potentiality<br>of the P-ISAR, for the imaging and classication purpose. In fact, by<br>using more than three adjacent channels and by observing the signal for<br>a long time, ner range and cross-range resolutions, respectively, could<br>be achieved. Finally, the obtained results on real data was discussed in<br>the chapter 6.