TIME-DOMAIN FIELDS EXTERIOR TO A 2-DIMENSIONAL FDTD SPACE

A transformation algorithm for the near-zone and far-zone fields exter ior to a two-dimensional (2-D) finite-difference time-domain (FDTD) fi eld lattice has been developed entirely in the time domain, The fields are found from a surface integration of the convolution of the time d erivative of equivalent currents and charges along a contour that encl oses the scatterer or radiator of interest. The kernel of the convolut ion integral has a square-root singularity for which an efficient nume rical integration rule is presented, Using this technique, a very accu rate solution is obtained; however, convolution integrals are computat ionally expensive with or without singularities, As an alternative, a rapidly convergent approximate series expansion for the convolution in tegral is presented, which can be used both in the near and far zone, Results using the new 2-D transform are compared with analytical expre ssions for the fields generated by a modulated Gaussian pulse for TE a nd TM line sources. In addition, the 2-D transform solution for the ne ar-zone fields scattered from an open-ended cavity for a TE incident m odulated Gaussian pulse plane wave is compared against a full-grid FDT D solution for accuracy and efficiency, The 2-D transform far-zone fie lds are compared against an alternative technique, which uses a double Fourier transform to perform the convolution in the frequency domain.