Waveform design for spaceborne synthetic aperture radar

Synthetic Aperture Radar (SAR), which was first developed in the 1950's as a technique for improving the resolution of military reconnaissance radar, has rapidly matured as a remote sensing tool for a wide range of civilian applications. Although the signal waveform is the very medium that delivers target information, little effort has been made yet on the aspect of waveform design and its influence on the generated SAR image. This thesis aims at addressing the role of waveform design in SAR, and developing new types of waveform that may suit some particular SAR applications. Several propositions are put forward in regard to the properties of the P code compression output and their corresponding proofs are provided accordingly. Based on the sidelobe formulation at the pulse compression output, a novel pulse compression technique is developed that produces an optimal uniform range sidelobe of the ideal Barker code level. The newly obtained sidelobe pattern provides an optimal compromise between the range resolution and the peak sidelobe level (PSL), regardless of the signal code length, and also retains the merit of strong resistance to the Doppler shift effect. Very low sidelobe regions appear around the mainlobe peak, which is useful in target tracking and recognition. When distributed targets are concerned, the integrated sidelobe level (ISL) is considered as a useful measure for the image quality. A novel processing technique is proposed to reduce the ISL energy. A sidelobe canceller is generated directly from the incoming signal and combined together with the original pulse compression output in which unwanted sidelobes are significantly eliminated. With the assumption that many dominant features found in images of urban areas originate from corner reflection phenomena, it is attempted to model the electromagnetic interaction of radar signals with urban structures. The new pulse compression technique successfully accommodates wide dynamic responses of the urban features and provides a high image contrast without sacrificing target resolution.