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Synthetic Aperture Radar Signal Processing with MATLAB Algorithms by Mehrdad Soumekh

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7

CIRCULAR SYNTHETIC APERTURE RADAR

Introduction

Synthetic aperture radar (SAR) research has been mainly focused on imaging and target recognition algorithms when spotlight or stripmap data collection is used. As we showed in Chapters 5 and 6, in these SAR systems a radar-carrying aircraft moves along a line while it illuminates the target scene; we refer to these imaging systems as linear SAR. One of the problems with a linear SAR system in the reconnaissance problems of SAR is that a target SAR signature, that is, the amplitude pattern an(ω, xn, ynu) with sufficiently high signal-to-noise power ratio, can be measured only over a limited aspect angle interval.

For example, in a stripmap SAR system with a planar radar aperture having a diameter comparable to the wavelength, the maximum aspect angle of the radar is approximately ±45 degrees; see Chapter 3. This limitation is mainly caused by the limited divergence angle of the radar radiation pattern a(ω, x, y). Chapters 5 and 6 provide discussions on this issue and show results where realistic FOPEN stripmap SAR data exhibited this phenomenon. (There are other factors that degrade the reconstructed images, such as commercial radio frequency interference.)

In the linear SAR systems, depending on what the angular orientation of the target is, the user could face a complicated matching algorithm in the aspect angle domain in order to determine the target type and its orientation. The matching algorithm may also be unreliable and ...

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