Theoretical Modeling of Multi-Sleeve Monopole Antennas

–This article presents a numerical technique based on the modal-expansion method,for modeling a multi-sleeve monopole an- tenna fed through an infinite ground-plane by a coaxial transmission line. The modal-expansion analysis is facilitated by introducing a per- fectly conducting boundary at a variable height over the ground-plane of the monopole. The resulting structure is then divided into a num- ber of regions and the electromagnetic field components in each region are expanded into the summation,of its modal functions. The cur- rent distribution over the monopole and sleeve surfaces as well as the antenna’s input impedance are computed by finding the expansion co- efficients through matching the tangential field components across the regional interfaces. Numerical results for the surface current distribu- tion and input impedance are presented and discussed with emphasis laid on single- and double-sleeve monopole antennas.