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Keywords: Radomes
Electromagnetic theory
Scattering and propagation
Numerical techniques
Issue Date: 1996
Abstract: An efficient generalized moment method which employs conjugate gradient and fast Fourier transform techniques (CG-FFT) is applied to compute the radar cross section (RCS) and transmission field distribution of small radomes with plane wave incidence. The analysis is based on an equivalent electric volumetric current model. The RCS prediction and transmission field distributions obtained show good agreement with the exact results for spherical radomes and data published for Von Karman radomes. In the numerical simulation, the volumetric current distribution of the radome is represented by three-dimensional roof-tops. The choice of three dimensional roof-tops as basis functions and pulses as testing functions to discretize the electric field integral equation (EFIE) yields a coupled set of integral equations. These matrix form equations are solved by an accurate and computationally efficient CG-FFT procedure which guarantees a monotonic decrease of the least squares error. Compared with the simple moment method using surface current equivalence which has been applied earlier to small radomes, the application of CG-FFT avoids the storage of large matrices and significantly reduces the computation time by an amount increasing with the number of Ns basis functions taken. For a problem where Ns basis functions are used to represent the current distributions, the memory storage required for this CG-FFT scheme is only of vectors of dimension Ns (five for the CG algorithm itself, plus some more to perform intermediate computations using FFT). In contrast, the memory requirement for the direct moment procedure is of a matrix with N2s elements. The total computation time for the CG-FFT scheme applied is about ANiNs log Ns, with Ni being the number of iterations required which is much smaller than Ns in this CG-FFT scheme and A a constant. However, with the direct moment method the CPU time needed for the same basis functions expansion follows the law BN3s + CN2s + DNs where B, C and D are constants. The application of volumetric current equivalence makes it easier to model the arbitrary geometries of small radomes than using surface current equivalence. Not only can it be applied to closed shells which is the case studied earlier using surface current equivalence, but also it can be applied to model open shells, where surface current equivalence finds difficulties. Volumetric current equivalence is found to be easier in handling inhomogeneous material composition as well. Taking Von Karman shape radomes as an example, the influence of the salient radome parameters such as radome thickness, material loss and presence of windows on the scattering and transmission properties of the radome with plane wave incidence are studied in the thesis. Based on the simulation results obtained, a discussion on convergence of applying the generalized moment method with CG-FFT scheme to small radomes is also presented.
Appears in Collections:Master's Theses (Restricted)

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