Scattering center parameterization of wide-angle backscattered datausing adaptive Gaussian representation

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     

Joint time-frequency ISAR using adaptive processing

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 aids 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 nonpointscattering 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     

Integral equation modeling of multilayered doubly-periodic lossy structures using periodic boundary condition and a connection scheme

This paper presents a boundary integral formulation to analyze multilayered doubly-periodic lossy structures with arbitrary geometry. The formulation is based on the moment method using first-order triangular patch basis functions. Each individual layer is analyzed separately using the simple free-space Green's function. After discretization, periodic boundary conditions are imposed on each region and a connection scheme is used to connect the regions. Metallic patches between layers or on the periodic boundary are also included in the model. Several examples are presented showing both the flexibility and the accuracy of the method.     

Shape optimisation of broadband microstrip antennas using geneticalgorithm

The genetic algorithm (GA) is used to design patch shapes for microstrip antennas on FR-4 substrate for broadband applications. Measurement results of the GA-optimised designs show good agreement with numerical prediction. The optimised patch design achieves a fourfold improvement in bandwidth when contrasted with a standard square microstrip antenna     

ASAR-antenna synthetic aperture radar imaging

The antenna synthetic aperture radar (ASAR) imaging concept is introduced. We present the ASAR imaging algorithm to pinpoint the locations of secondary scattering off a platform from antenna radiation data. It is shown that a three-dimensional (3-D) ASAR image of the platform can be formed by inverse Fourier transforming the multifrequency, multiaspect far-field radiation data from an antenna mounted on the platform. This concept is demonstrated using the computed radiation data from the code Apatch, which employs the shooting and bouncing ray (SBR) technique. Furthermore, we develop a fast ASAR algorithm specially tailored for the SBR approach. By taking advantage of the ray tracing information within the SBR engine, we demonstrate that the fast approach can result in the same quality of image as the frequency-aspect algorithm at only a fraction of the computation time     

Interpretation of scattering phenomenology in slotted waveguidestructures via time-frequency processing

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