Printed dipole antennas find increasing use in microwave as well as far infrared frequencies. The current distribution, input impedance, and radiation pattern are computed for wire antennas printed on a dielectric substrate. The current distribution is obtained by solving Pocklington's equation by moment methods. The Green's function pertinent to the problem involves improper Sommerfeld-type integrals. These integrals are computed by a real-axis integration technique which involves analytical and numerical steps. The effect of surface modes is carefully taken into account.

Current distribution and input impedance of printed dipoles

The problem of a monopole antenna mounted near or at the edge of a half-plane is solved using a hybrid moment method solution with an integral expression for the exact half-plane Green's function. Results are presented for input impedance of a \lambda/4 monopole versus distance from the half-plane edge and versus angle for an edge-mounted antenna, Simple expressions for the surface current density induced on the half-plane are derived, and an attachment mode is constructed for use with the author's previously developed surface patch moment method solution when a wire is attached at or near an edge of a finite plate. Results obtained from the MM/GTD method are also presented for comparison.

Analysis of a monopole mounted near or at the edge of a half-plane

The effect of the thickness and relative permittivily of a dielectric cover on a printed microstrip dipole has been analyzed. It is shown that the current distribution and the input impedance are, in general, very sensitive to variations of the cover parameters. For a dielectric plate with a constant thickness the dipole resonant length decreases substantially with an increase of the relative permittivity. Because of the limited bandwidth presented by single-element microstrip antennas the effects of the dielectric cover on the design of these antennas have to be carefully considered. For the calculation of the current distribution, the Hertz vector potential associated with the problem was determined for an element of current located in a stratified medium with four layers. Pocklington's integral equation was solved for the currents, using Galerkin's method with piecewise-sinusoidal expansion and weighting functions.

The effect of a dielectric cover on the current distribution and input impedance of printed dipoles

A marching-on-in-time (MOT)-based volume-surface integral equation (VSIE) method is introduced to analyze transient electromagnetic scattering from the composite structures comprising perfect electrically conducting (PEC) bodies and inhomogeneous dispersive dielectric materials. A recursive convolution scheme is employed to deal with dispersive materials. The plane-wave time-domain (PWTD) algorithm is incorporated to accelerate the MOT scheme. In our examples, Debye, Lorentz, and Drude models are used to analyze the dielectric materials of the composite objects, respectively. Numerical results are given to demonstrate the accuracy and efficiency of the proposed scheme.

Analysis of Scattering From Composite Conducting Dispersive Dielectric Objects by Time-Domain Volume-Surface Integral Equation

Mutual coupling between two dipole antennas with different dimensions placed at arbitrary parallel positions is analyzed using simultaneous integral equations with exact kernels and finite gap feeds. The Nystrom method is applied to solve these equations. Self- and mutual-impedances are calculated and compared with the results of the induced electromotive force (EMF) method and Tai’s method. The feed structure is accurately modeled, and S-parameters are calculated based on the model. The S-parameters are measured, and the results are compared with the calculated values. They show good agreement, and the validity of this method is verified.

Analysis of Mutual Coupling Between Dipole Antennas Using Simultaneous Integral Equations With Exact Kernels and Finite Gap Feeds

Closely spaced thin-wire antennas are analyzed by the moment method using the piecewise-sinusoidal function to describe the current variation along the length of the wire and a Fourier series for the circumferential variation. Data are presented for the circumferential variation of the surface current density of parallel dipoles obtained by the "thin-wire" theory, wire-grid model, and the present formulation. It is found that there is substantial circumferential variation, even for dioples spaced more than several wire diameters.

E. Newman

Papers

The circumferential variation of the axial component of current in closely spaced thin-wire antennas