Analysis of coaxially fed monopole antennas using an auxiliary sources technique

Abstract

[1] In this paper, the radiation from a circular cylindrical monopole fed through a perfectly conducting ground plane by a coaxial transmission line is analyzed using the method of auxiliary sources. The proposed method is applied by introducing a set of fictitious sources aligned with the monopole's axis for the direct description of the radiated electromagnetic field above the ground plane, under the assumption of a single transverse electromagnetic mode existing in the annular aperture of the line. The currents of the fictitious sources are derived by imposing the continuity condition of the tangential electric field on the physical surface of the dipole. For the occasion, the fictitious sources are chosen to be spatially overlapped sinusoidal dipoles. It is substantiated that this choice results in a noteworthy acceleration of the convergence rate of the solution in comparison with the one associated with infinitesimal dipoles, which are usually used in currentmodel-based techniques. Since the currents of the fictitious sources are determined, pertinent quantities of great interest, including the current distribution along the monopole, the input impedance/admittance, and the field intensities in the near and the far region, can be determined in a straightforward manner. Several examples concerning various geometries are established and compared with previously published data.

Comments on “Fundamentals of Thin-Wire Integral Equations With the Finite-Gap Generator”

“…We were not previously aware of these interesting and noteworthy papers, which seem to be the first to use what we, in [3] and [4], call the "effective current." Despite this similarity, the overall purpose of our [3] and [4], as well as that of the related works [5] and [6], is quite different from that of [1] and [2]. References [3]- [6] use the effective current in order to overcome difficulties specifically associated with unsolvability (rather than with matrix ill-conditioning, or other shortcomings of computer hardware or software).…”

“…(ii) A difference of a factor of ½ near the driving point; this difference concerns the imaginary part of the current in the delta-function generator case [5], and the imaginary part of the derivative of the current, or the charge per unit length, in the case of the finite-gap generator [3]. Still for the infinite antenna, an important similarity [3], [5] is that the real parts of the exact and effective currents are (exactly) equal. Such results have no counterparts in [1] and [2].…”

“…For the infinite-length antenna, perhaps the two most striking differences are: (i) The effective current equals the current on the outer surface of the antenna [4] (on the other hand, it is well-known that the exact current equals the total ( ) current). (ii) A difference of a factor of ½ near the driving point; this difference concerns the imaginary part of the current in the delta-function generator case [5], and the imaginary part of the derivative of the current, or the charge per unit length, in the case of the finite-gap generator [3]. Still for the infinite antenna, an important similarity [3], [5] is that the real parts of the exact and effective currents are (exactly) equal.…”

On the combination of the method of auxiliary sources with reaction matching for the analysis of thin cylindrical antennas

“…Although the fundamental ideas behind the MAS are quite simple, there are many important aspects, such as the type of the auxiliary sources, the locations of the auxiliary sources and matching points, as well as the correlation between them and the convergence behaviour of the solution, that render the application of the method non-trivial [9]. For details on the application of the MAS to thin wire antennas refer to References [13,14]. Herein, the dipole under consideration is modelled with the aid of an axial set of auxiliary sources.…”

“…Herein, the dipole under consideration is modelled with the aid of an axial set of auxiliary sources. For reasons that are related to the convergence behaviour of the method and the quality of the solution with regard to the satisfaction of the electric field boundary condition [13,14], the auxiliary sources are selected to be idealized sinusoidal dipoles instead of elementary dipoles that are usually used in the MAS [9]. The auxiliary dipoles are spatially overlapped in a manner that the centre of each one is placed exactly at the ends of the two adjacent ones, as shown in Figure 2.…”