EFFICIENT EVALUATION OF NEAR-FIELD TIME-DOMAIN PHYSICAL-OPTICS INTEGRAL USING LOCALLY EXPANDED GREEN FUNCTION APPROXIMATION

A time-efficient method is proposed to calculate the near-field time-domain physical-optics (TD-PO) integral to analyze the transient electromagnetic fields scattered from three-dimensional perfectly conducting objects under the illumination of a pulsed plane wave. It is shown that the TD- PO integral can be reduced to a close-form expression by introducing locally expanded Green-function approximations used in conjunction with the surface partitioning. As a result, the near-field TD-PO response to a general pulsed plane wave excitation is derived by a convolution of the excitation waveform with the TD-PO impulse response, which can be performed in a closed form. To satisfy the causality, i.e., the transient field cannot travel away from the sources faster than the speed of light, the high-order derivative of a modulated-Gaussian wave is specified as the excitation waveform. The efficiency and accuracy of the proposed near-field formulas are validated through numerical examples.