Improved complex images of a magnetic dipole in a parallel-plate waveguide

The vector and scalar potential Green´s functions of a dipole source in a parallel-plate waveguide (PPW), can be expressed in either an infinite image expansion or an infinite modal expansion. However it is well known that the image expansion and the modal expansion converge very slowly when the observation point is far from the source point and close to the source point respectively. Recently in order to derive closed form Green´s functions which converge rapidly over the whole spatial range, the complex image method for the horizontal electric dipole in a PPW was proposed by Yang et al. (1992). Here a complex image method to derive closed form Green´s functions for the analysis of an electromagnetic pulse (EMP) coupling problem via an aperture into PPW, is considered. However we have observed that the previous method is only useful in deriving the expressions at low frequencies. As the frequency increases, the previous method has the difficulty of approximating the spectral Green´s functions in terms of complex exponentials, because it is very difficult to find the adequate approximation parameter (e.g., truncation point T/sub 0/). In this study a complex image which is useful in deriving closed-form expressions to give more accurate results than previous results for the Green´s function of a horizontal magnetic dipole in a PPW over a wide frequency range as well as the whole spatial range, is considered.