الفهرس | Only 14 pages are availabe for public view |
Abstract This thesis addresses Synthetic Aperture Radar (SAR) for high resolution microwave land imaging. The SAR is radar used to create an image of object by using use of relative motion, between an antenna and the target region to obtain finer spatial resolution than is possible with conventional beam-scanning means. SARs image has two spatial dimensions, one dimension in the image is called range (or cross track) and is distance from the radar to the target. SAR range resolution is determined by the transmitted pulse width, i.e. narrow pulses yield fine range resolution. The other dimension is called azimuth (or along track) and is perpendicular to range. To obtain fine azimuth resolution, a physically large antenna is needed to focus the transmitted and received energy into a sharp beam. The sharpness of the beam defines the azimuth resolution. The present thesis is concerned with enhancing the SAR imaging resolution in both range and azimuth directions. It proposes a new scheme for SAR pulse compression to get high resolution images in the range direction. The principle of a chirped pulse with quadratic frequency modulation (QFM) is introduced as a way for achieving fine SAR imaging resolution and good signal to noise ratio. Side lobe level reduction of the matched filter response due to the received compressed pulse is achieved using a single stage of a second order time-dependence of the frequency. The parameters of time-dependence of the frequency are shown to have a great effect on the lowest side lobe level of the time waveform of the signal at the output of the matched filter and on the received pulse width as well. Simulation results of the proposed QFM compressed signal are presented, where suppressed side lobe level is achieved. High-resolution wide-swath imaging using SAR system requires a radiation beam which is narrow in the azimuth direction and relatively wide in the range direction. Moreover. along the range direction. the signal strength should be uniform over the beam spot area on the ground surface. Such a beam is very difficult to implement unless an array with large number of elements and an optimized distribution |