Accurate analysis of metallic TEM horn antennas for pulse radiation using the FDTD method

In its basic form, the TEM horn antenna consists of two thin, metallic sheets, each an isosceles triangle with the angle at the apex being /spl alpha/, The planes of these triangles are separated by the angle /spl beta/, and the antenna is fed with a transmission line connected at the apices. The authors present a sketch of the image equivalent for this antenna: a single triangular sheet over a metallic image plane. For many years, the TEM horn has been used to radiate and receive pulsed signals. Its performance has been optimized for this purpose by modifying the basic structure described. The design and optimization of these antennas, however, has been largely by empirical means, with no accurate, comprehensive electromagnetic analysis of the complete structure. The purpose of the present paper is to present an analysis, based on the finite-difference time-domain (FDTD) numerical method, for the basic metallic TEM horn and to verify the analysis with accurate measurements. Graphical displays of the electric field in the space surrounding the horn for the times of interest help explain the operation of the antenna and suggest possible modifications for improving its performance.