I. Introduction
In past years, many higher order finite-difference time-domain (HO-FDTD) methods [1]–[7] have been developed to improve the accuracy of the FDTD methods [8]–[13]. These HO-FDTD methods use higher order finite-difference approximations for the space derivatives to improve the accuracy of the FDTD methods. Further, parametric optimization techniques such as the improved FDTD methods [14], [15] and (2, 4) stencil FDTD methods [16]–[18] have also been proposed to improve the accuracy of the FDTD methods. However, these parametric optimization techniques give improved accuracy around any given frequency only.