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The article presents a new approach that can be used for an improved analysis of the periodic permanent magnet (PPM) focusing structure for the linear beam tubes. The approach is shown to include the effects of the magnetic saturation in the iron pole pieces as well and hence is extremely accurate.

In this paper, we present and compare two techniques of discriminating complex objects, using the electromagnetic scattering response in the time and frequency domains. The scattering in the time and frequency domains are computed using the Finite Difference Time Domain (FDTD) method and the Method of Moments (MoM), respectively. The dominant Natural Resonant Frequencies (NRFs) of the objects have been identified, using the Matrix Pencil of Function (MPoF) algorithm from the scattering response in the time domain, and the Vector Fitting (VF) method using the response in the frequency domain. The dominant NRFs in both cases have been identified after thresholding the power contribution of each pole. A "Risk" function using the dominant poles of any two scattering objects is then defined, which aids in quantifying the discrimination. Perfectly Electrically Conducting (PEC) objects with minor variations in their geometric shape have been discriminated using the risk function. It is shown that the techniques described in this paper are effective in discriminating targets. Both approaches, using the time and frequency domain scattering response are found to yield identical results. A single run of the FDTD algorithm is sufficient to compute the electromagnetic response required to determine the dominant natural resonances. Hence, the approach of using the time domain scattering response is computationally efficient. Thus a hybrid approach of computing the resonances from the time domain scattering response and discrimination using the risk function defined, is fast enough to apply to targets of realistic size such as an aircraft at operational radar frequencies. [ABSTRACT FROM AUTHOR]