The axis boundary condition scalar potential integral equation is used to study the hemispherically capped thick cylindrical monopole with a conical feed section. The monopole is perfectly conducting and is fed by a coaxial line whose outer radius is connected to an infinite perfectly conducting ground plane. One approximation in the equation is that the field across the coaxial aperture is approximated by the fundamental TEM coaxial line mode. The integral equation is numerically solved by the moments method using entire domain basis functions with delta weights. A simple way for checking the convergence of the solution that needs no new integrations is given. The theoretical current distributions, input admittances, and radiation patterns are given for a thin, moderately thick, and thick monopole with and without a conical feed section. This feeding section simplifies the matching of the antenna to conventional signal generators and improves the high frequency characteristics of the monopole.

Hemispherically capped thick cylindrical monopole with a conical feed section

The radiation field pattern of a flush-mounted coaxial aperture is derived in the frequency domain. By using the Lorentz reciprocity theorem, the equivalent current generator is obtained which drives the apparent annular antenna admittance in shunt with the load admittance. The current source, aperture admittance, and load admittance determine the transfer function. The transfer function multiplied by the expression for the spectrum of the incident pulse forms the integrand of the Fourier transform from which the time history of the current waveform in the load admittance may be obtained using a computer. There are several applications of the theory. The one of dominant interest at present may be described as follows. A coaxial transmission line terminated in a known load admittance is located in the interior of a missile. The free end of the cable forms an aperture antenna at the skin of the missile, i.e., at the normal junction of coaxial connectors. The problem is to determine the time history of the current in the load admittance when an intense transient electromagnetic field impinges on the receiving antenna. Very accurate numerical results may be obtained from this theory provided the ground plane is sufficiently large and certain dimensional limitations on the sizes of the inner conductor and sheath of the coaxial aperture (expressed in terms of the wavelength) are met.

On the Pulse Response of a Flush-Mounted Coaxial Aperture

The effect of dielectric loading on the electromagnetic radiation characteristics of thick monopole antennas is investigated. A surface integral equation formulation for a dielectric-loaded thick monopole antenna modeled as a body of revolution is presented. The surface integral equations were solved via the method of moments for the unknown surface current distributions. The numerical data were verified by comparison of the results for input impedance with data available in the literature and with measured data for different configurations. The effects of loading on the input impedance, bandwidth, and beamwidth are considered for antennas mounted on both infinite and finite ground planes. Loads of various shapes and dielectric constants are investigated. Numerical results are presented for various conical and wire monopoles loaded with dielectrics which may partially or completely cover the conducting surface of the antenna. >

Electromagnetic characteristics of a thick monopole antenna with dielectric loading

The problem of a buried axial Hertzian dipole placed at the end of a semi-infinitely long metallic tube is associated with the investigation of electromagnetic through-the-earth propagation. Under a thin-tube approximation explicit analytic expression of the far-field is obtained by employing the Wiener-Hopf technique. Numerical results are presented in this paper for various dipole locations and ground conductivities. The improvement over the result based upon a Kirchhoff's approximation is noted.

Radiation of a buried dipole in the presence of a semi‐infinite metallic tube

Since the inception of short range Ultra Wideband (UWB) communication systems the factors like device miniaturization and high speed data rate create big challenges for antenna designers. One way to make the design job easy is to statistically model the variabilities of antenna radiation behavior as a function of its geometry. Such an effort is also useful for the better usage of the communication channel by combining the antenna model with it. This thesis is an attempt towards statistical modeling of UWB antennas. The subject faces two main challenges, the creation of sizeable statistical population of the class of antenna design(s) and modeling of antenna's radiation pattern which is composed of huge number of complex parameters. In this thesis we try to answer the former by proposing a generic design approach for UWB planar antennas and the latter by presenting the use of ultra-compressed parametric modeling technique. The generic design approach is based on trapezoidal shapes and offers great flexibility and versatility in designing various UWB antennas. This approach shows a significant ease in antenna optimization (also for population creation) as it reduces the no. of parameters that controls the antenna geometry without compromising the degree of freedom. Ultra-compressed parametric modeling is based on two antenna synthesis methods, singularity expansion method (SEM) and Spherical mode expansion method (SMEM) that reduce the required no. of complex parameters for the radiation pattern by 99.9%, making the modeling effort possible. A statistical model of biconical antenna based on ultra-compressed modeling technique has been presented.

Parametric Modeling of small terminals and Multiband or Ultra wideband Antennas

The complete radiation field of a tubular monopole of arbitrary length and radius, which is base driven by a low-impedance coaxial transmission line, is derived. The integral equation for the current distribution, which includes a term for the feed-point correction is solved by the inversion of a matrix under the assumption that the current is a continuous, piecewise linear function. The far-zone electromagnetic field established by this current is expressed in closed form. It is found that the effect of thickness is to round off the nulls predicted by previous theory for vanishingly small radius and to enhance the high-angle radiation.

E. Aronson

Papers

Tubular monopole of arbitrary dimensions: The radiation field