Modal-Expansion Analysis of Electromagnetically Coupled Coaxial Dipole Antennas

Zhongxiang SHEN  Quanxin WANG  Ke-Li WU  

IEICE TRANSACTIONS on Communications   Vol.E89-B   No.5   pp.1654-1661
Publication Date: 2006/05/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.5.1654
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Antennas and Propagation
antennas,  dipole antenna,  electromagnetically coupled coaxial dipole,  modal-expansion method,  

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This paper presents a modal-expansion analysis of the electromagnetically coupled coaxial dipole antenna. The analysis of the antenna problem is initially simplified using the even-odd mode excitation and then the resultant half structure is divided into two parts; one is the characterization of a coaxial feeding network and the other is the modeling of a sleeve monopole antenna driven by a coaxial line. The formally exact modal-expansion method is employed to analyze both parts. The analysis of the sleeve monopole antenna is facilitated by introducing a perfectly conducting boundary at a distance from the monopole's top end. The current distribution and input impedance of the electromagnetically coupled coaxial dipole antenna are obtained by finding expansion coefficients through enforcing the continuity of tangential field components across regional interfaces and cascading the two parts together. Numerical results for the coaxial dipole antenna's radiation characteristics are presented and discussed.