Theory of a multiply fed and loaded insulated linear antenna in air

Analytic expressions are derived for the input admittance and the current distribution along the multiply fed and loaded insulated antenna in air which is excited across feed gaps of nonzero widths. The Wiener-Hopf type analysis for a center fed insulated antenna is combined with the axial field discontinuity (AFD) method to develop the current and admittance expression. This AFD method considers the metallic surface of the linear antenna as a series combination of longitudinal, electric-field surface functions that exist due to feeding and/or loading. The analysis, which does not employ superposition of even and odd distributions of sources and loads, yields final expressions in terms of the excitation location, its aperture electric field within the feed gaps, impedance locations, and their values. The current distribution for cases of unity dielectric constant shows an excellent agreement with data based on the moment method. The input admittances and current distributions are reported for different multiple excitations and loads and dielectric constants of the insulator     

Input admittance of a biconical antenna with wide feed gap

The biconical antenna fed across a wide feed gap is studied as a boundary-value problem, using modal analysis. The study deals with finite-length antennas. It also includes the consideration of two limiting cases of biconical antennas, i.e. wide angle (spherical antennas) and very small angle (thin wire antennas). Expressions for the input as well as apparent terminal admittances are derived and corresponding values compared with available literature data for vanishingly small feed gap widths (delta function generator)     

Feed gap aperture field and input admittance of an infinitely longinsulated antenna

Expressions are derived for the input admittance and aperture electromagnetic fields in the feed gap of a solid insulated antenna of infinite extent. This is done by solving the boundary value problem where the fields are represented by Fourier series built up by superposition of basic sets of φ-independent cylindrical waves. Such waves are obtained from the solution of the Helmholtz equation governing the z-directed electric Hertzian potential. The axial aperture electric field in the gap is in the form of a Fourier-Bessel series and is used to find the input admittance. Results are plotted for the aperture fields and tabulated for the input admittances at different radii, insulating shell dielectric constants, and gap widths     

On the Wiener-Hopf analysis of thick solid antenna with nonzerofeed gap width

Hurd's Wiener-Hopf-type analysis for the admittance of a long, thin, tubular antenna is extended to the case of an electrically thick solid antenna. Expressions for the input admittance and the current distribution along a solid dipole antenna without restriction on the thickness are presented. It is found that as with thin antennas, using one term of the final solution asymptotic series also produces accurate results for thick long antennas. It is found that two series terms have to be used when the antenna is short     

Wiener-Hopf type analysis of dielectric-coated dipole antenna inrelatively dense medium

The problem of dielectric-coated dipole antennas in a relatively dense medium is solved using the Wiener-Hopf technique. The analysis is done for a perfectly conducting dipole antenna coated by a low-loss dielectric and embedded in a lossy medium of a wavenumber larger than that of the lossy coating. Analytic expression are derived for the input admittance and the current distribution along the dipole which is excited at the center across a nonzero width feed gap. Results are compared with available literature data for different antenna lengths embedded in an ambient medium with a loss tangent of σ/ω∈. The numerical work involves only the determination of certain integrals using standard integration routines     

Optimal design of multiply fed dipole antennas

The gain of a mulitply fed dipole antenna of lengthL, small radiusaand arbitrary locations of feed voltages along the antenna is computed using the well-known moment method. An optimization routine is then employed to study the possibility of maximizing the gain in a specified angular direction and minimizing it at other directions for any given number of excitations and antenna length in order to determine the optimum complex values and location of each source. The results are presented in tables and graphs for a wide range of antenna length and number of feeds. It is shown that both the gain and beamwidth are improved by this technique at the expense of appearance of new sidelobes and requirement to design a more complicated feed network. The Fourier series expansion method is extended in order to determine the gain of a multiply fed wire antenna, and the results for the radiation pattern show good agreement with those based on the moment method.     

Rigorous analysis finite length insulated antenna in air

A Weiner-Hopf-type analysis is used to solve the problem of a dielectric coated dipole antenna in free space. Analytic expressions are derived for the input admittance and the current distribution along a center-fed antenna excited across a gap of nonzero width. Such expressions are represented in terms of a function representing the aperture-gap field, which is considered equal to that at the gap of a similar solid insulated antenna with infinite extension. Results are in very good agreement with reported experimental results at different outer radii and dielectric constants of the dielectric coating for different antenna lengths. The numerical work involves only the determination of certain integrals using standard integration routines