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A study was conducted to analyze the antenna synthetic aperture radar (ASAR) imaging concept. The three-dimensional ASAR image of a platform was formed by inverse Fourier transforming and multifrequency, multiaspect far-field radiation data from an antenna mounted on the platform. An ASAR algorithm was developed for the shooting and bouncing ray method. Results indicated that the fast approach supports similar quality images as the frequency-aspect algorithm with reduced computation efforts.

We present a scattering center extraction algorithm to parameterize the backscattered data from complex targets collected over large angular apertures. This parameterization is based on a scattering center model of the target, but includes an aspect-dependent amplitude function for each scattering center. A two-dimensional (2-D) adaptive Gaussian representation (AGR) algorithm is used to extract the position and the amplitude function associated with each scattering center. The algorithm is tested with data generated by the Xpatch radar simulation code as well as chamber measurement data. The results show that a very good compression ratio can be achieved, resulting in a compact scattering center model of the target. Once such model is available, we can easily reconstruct range profiles and ISAR images at any aspect on the same plane with good accuracy. Index Terms - Electromagnetic scattering inverse problems.

A new joint time-frequency inverse synthetic aperture radar (ISAR) algorithm that combines ISAR processing with the joint time-frequency signal representation is presented as a means of extracting the nonpoint-scattering features from the standard ISAR image. The adaptive Gaussian representation, applied to the range axis of the ISAR image, is used as the time-frequency processing engine. This technique uses Gaussian basis functions to adaptively parameterize the data and, as a consequence, the point-scattering mechanisms and resonance phenomena can be readily separated based on the width of the Gaussian bases. The adaptive joint time-frequency ISAR algorithm is tested using data generated by the moment-method simulation of simple structures and the chamber measurement data from a scaled model airplane. The results show that nonpoint-scattering mechanisms can be completely removed from the original ISAR image, leading to a cleaned image containing only physically meaningful scattering centers. The nonpoint-scattering mechanisms, when displayed in the frequency-aspect plane, can be used to identify target resonances and cutoff phenomena. Index Terms - Electromagnetic scattering inverse problems.

The scattering phenomenology in slotted waveguide structures is investigated using time-frequency processing of numerically simulated data. Two geometries are studied, a finite waveguide with one slot on each end and a linear slotted waveguide array comprised of 16 equally spaced slots. The numerical simulation is accomplished via a three-dimensional moment-method procedure in conjunction with a connection scheme which makes possible the simulation of a long waveguide structure spanning over 32 wavelengths at 10 GHz. The resulting numerical data are then processed using the short-time Fourier transform to identify the dominant scattering mechanisms. In the joint time-frequency plane, the unique scattering physics associated with slotted waveguide structures are more clearly revealed. In particular, the Floquet harmonics due to the exterior slot structure, the dispersion due to the interior waveguide modes, and the 'interior Floquet' phenomenon can be readily identified and fully interpreted.