A speedy computation of the time-domain Green's function for microstrip str
uctures is performed. The spatial Green's function in the frequency domain
is written as the sum of real- and complex-image terms. which are respectiv
ely converted into the time domain analytically and numerically via fast Fo
urier transforms. The coefficients of the complex-image terms are both spac
e and frequency independent and are computed only once, which results in a
speedy algorithm.