We present two methodologies that improve the performance of the alternating-direction-implicit (ADI) finite-difference time-domain (FDTD) scheme. The first one exploits optimized spatial operators and implements an artificial-anisotropy approach, so that errors around a central frequency are minimized. According to the second scheme, a matching-terms procedure is applied to the dispersion relation, so that approximations that improve space-time errors in a wideband fashion are obtained. The successful implementation of these principles is validated theoretically, while numerical tests reveal their advantageous properties in practical simulations.
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