Abstract-We propose an improved method of iterative physical optics (IPO) to analyze electromagnetic scattering by open-ended cavities.The traditional IPO method uses a fixed number of iterations; if this number is too small, the accuracy of the estimated monostatic radar cross section (RCS) of open-ended cavities degrades as the incident angle of the incident field increases. The recentlyintroduced adaptive iterative physical optics-change rate (AIPO-CR) method uses a variable number of iterations; compared to the IPO method, it predicts monostatic RCS more accurately, but requires more computation time. In this paper, a new algorithm is devised to improve both the monostatic RCS prediction accuracy of the IPO method, and the computational efficiency of the AIPO-CR method. The proposed method, iterative physical optics-retained previous solution (IPO-RPS), calculates the currents at one incident angle, then reuses them as the initial currents of iterations for the next incident angle. In simulations of the monostatic RCS for various open-ended cavities, the IPO-RPS method was more accurate than the traditional IPO method, and computationally more efficient than both the IPO and AIPO-CR methods.

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Abstract-In this paper, electromagnetic scattering problems are analyzed using an electric field integral equation (EFIE) formulation that is based on loop-star basis functions so as to avoid low-frequency instability problems. Moreover, to improve the convergence rate of iterative methods, a block matrix preconditioner (BMP) is applied to the EFIE formulation based on loop star-basis functions. Because the matrix system resulting from the conventional method of moments is a dense matrix, a sparse matrix version of each block matrix is constructed, followed by the inversion of the resultant block sparse matrix using incomplete factorization. Numerical results show that the proposed BMP is efficient in terms of computation time and memory usage.

A paraboloidal reflector antenna is useful for enhancing the directivity of a feed antenna with a low directivity. In this letter, we investigate a paraboloidal reflector antenna that has an ultrawideband (UWB) omnidirectional radiative source as the focal feed. To obtain the optimized focal length for a given diameter of the paraboloidal reflector antenna, we employ a simple relation between and , which can reduce the spreading loss of the source field while maintaining the aperture field uniformity. Simulation results show that the values obtained from the above relation can maximize the far voltage-a well-known figure of merit for UWB applications.Index Terms-Electromagnetic pulse (EMP), far voltage, integrated antenna-source (IAS) system, time domain, ultrawideband (UWB).

HANBIT is a magnetic mirror confinement device. Recent physics experiments have been mainly focused on identifying discharge characteristics and on getting stable plasma production and operation modes, by using a 500 kW slot antenna system at a fixed RF frequency of 3.5 MHz and varying discharge conditions such as fueling rate, RF power, and B-field intensity in central cell. Two distinct operation modes are found to be very sensitive to the RF power as well as the ratio of the RF frequency to the ion cyclotron frequency. A MHD interchange mode of m = -1 is clearly observed and the stabilizing mechanism can be explained by the sideband coupling theory.