Browsing by Subject "scattering problems"

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    Memory-efficient multilevel physical optics algorithm for the solution of electromagnetic scattering problems
    (2007) Manyas, Kaplan Alp
    For the computation of electromagnetic scattering from electrically large targets, physical optics (PO) technique can provide approximate but very fast solutions. Moreover, higher order approximations, such as physical theory of diffraction (PTD) including the diffraction from the edges or sharp corners can also be added to the PO solution in order to enhance the accuracy of the PO. On the other hand, in real-life radar applications, where the computation of the scattering pattern over a range of frequencies and/or angles with sufficient number of samples is desired, further acceleration may be needed. Multilevel physical optics (MLPO) algorithm can be used for such applications, in which a remarkable speed-up can be achieved by evaluating the PO integral in a multilevel fashion. As the correction terms like PTD are evaluated independently just on the edges or sharp corners, whereas the PO integration is carried out on the entire target surface, PO integration is the dominant factor in the computational time of such higher order approximations. Therefore accelerating the PO integration will also reduce the computational time of such higher order approximations. In this thesis, we propose two different improvements on the MLPO algorithm.First improvement is the modification of the algorithm that enables the solution of the scattering problems involving nonuniform triangulations, thus decreasing the CPU time. Second improvement is the memory-efficient version, in which the O (N3 ) memory requirement is decreased to O (N2 log N). Efficiency of the two proposed improvements are demonstrated in numerical examples including a reallife scattering problem, with which the scattering pattern of a three-dimensional stealth target is evaluated as a function of elevation angle, azimuth angle, and frequency.