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Precise Admittance of a Monopole.

Description: The purpose of this paper is to obtain the admittance of a monopole antenna to a higher degree of accuracy than has heretofore been reported in the literature. The model selected for analysis consists of a base-driven monopole of arbitrary dimensions (length and radius) protruding perpendicularly from an infinite ground plane. The transmission line providing the excitation is a coaxial cable with outer sheath truncated at ground level. The problem is solved by obtaining the admittance of the monopole of finite length for TEM excitation alone from an integral equation for the current that has a solution. The requisite information needed to modify this admittance to incorporate the localized cable-monopole junction or feedpoint effect is obtained from the solution of two ancillary problems. One of these problems consists of deriving an expression for the apparent admittance of an infinite monopole considering the TEM and higher order modes of type TM {sub on} (n=1,2,...) set up in the coaxial cable by the sheath discontinuity. In essence, this involves solving an integral equation for a function equal to the integral of the electric field across the feedpoint gap. The other supplementary problem requires finding the admittance of an infinite monopole for TEM excitation alone. This is achieved by suitably modifying the integral equation for determining the admittance (for TEM excitation) of the finite structure. Extensive numerical results in tabular and graphical form are provided in the paper. TM {sub on} modes in the coaxial cable to n = 400 are included in the admittance data. (auth)
Date: August 30, 1968
Creator: Chang, D. C. & Harrison, C. W., Jr.
Partner: UNT Libraries Government Documents Department