  The objective of the study is to assess the accuracy of a standard FDTD code
in description of high-Q resonances such as whispering-gallery-mode (WGM) ones
excited in circular dielectric resonators. To achieve the goal, we consider
circular resonators excited by line currents and extract the data on FDTD
accuracy from comparisons between the FDTD-solution and the exact one obtained
by the Mie-series solutions. The near-field and far-field characteristics are
studied for resonators of various sizes, made of quartz and silicon. Both E -
and H - polarizations are considered. The computational error, i.e. a resonance
frequency shift observed for the FDTD solution, is analyzed and compared for
several WGMs having different Q-factors.
