Analysis of antenna transient radiation

Abstract

Recently a new formalism has been developed for modeling time domain radiation processes in complex antennas. Using this formalism the radiated electromagnetic field can be expressed in terms of non uniform spherical wave contributions relevant to the resonant phenomena occurring in the structure. The developed algorithm consists of a dedicated two-step vector fitting procedure. Firstly, the spherical harmonic expansion of the time-domain equivalent electric and magnetic currents is performed. Then, by using the Singularity-Expansion-Method (SEM), the time-variant spherical harmonic expansion coefficients are represented in terms of dumped exponential terms. In this way, by using the incomplete modified spherical Bessel functions, an analytical description of the transient wave radiation phenomena is achieved. In this study several canonical radiating structures such as dipole, bow-tie and loop antennas, have been analyzed using the afore-mentioned formalism in order to gain a physical insight into the natural resonant processes occurring in the antenna and find a relation with the relevant geometrical characteristics.