A. T. Adams

Single-Post Inductive Obstacle in Rectangular Waveguide

A rapidly converging moment solution for electromagnetic scattering by a single inductive post in a rectangular waveguide is obtained. The numerical results show good agreement with Marcuvitzs data as far as this data goes. Furthermore, Marcuvitzs curves are extended to cover data for large posts. This new data should aflow one to design a simply constructed new type of narrow bandpass filter, namely, a filter consisting of large single posts. The successful use of this straightforward moment solution in solving the single-post problem suggests that this technique should prove useful in solving a variety of microwave discontinuities such as those involving thin or thick irises and posts of arbitrary shape.

Computation of the Capacitance Matrix for Systems of Dielectric-Coated Cylindrical Conductors

The method of moments is applied to the computation of the charge distributions and capacitance matrix for electrostatic systems of bare and dielectric-coated cylindrical wires. Several choices of expansion functions are investigated in detail and compared. Harmonic series expansion functions are shown to be especially well suited to problems involving systems of closely-spaced dielectric-coated cylindrical wires.

The quadrifilar helix antenna

The characteristics of the quadrifilar helix antenna [1] and [2], a broad-band high-gain device, are described in detail. Experimental data on beam patterns, impedance, and axial ratio are given for both the circularly polarized quadrifilar helix antenna (QHA) and the linearly polarized counterwound quadrifilar helix antenna (CQHA). Bandwidths in excess of 5:1 are obtained. The low frequency behavior is discussed. Computation of the QHA characteristics by moment methods [3] is described and computed data on beam patterns and current distributions are given.

Flush mounted rectangular cavity slot antennas--Theory and design

The loaded rectangular cavity slot antenna is analyzed using variational methods in conjunction with simplified equivalent circuit techniques to derive accurate design guides for efficiency, bandwidth, and resonant frequency. The aperture admittance is computed and the effects of a compound aperture plane iris and of material loading are analyzed. The aperture admittance of all such loaded cavity antennas is proportional to \mu_{r} , \sqrt{\mu_{r}/\epsilon_{r}} , or 1/\epsilon_{r} , which characteristic lends to a common method of optimization of |T|^{2} (transmission cofficient). Experimental results include: 1) measurements of aperture field; 2) a comparison of theoretical and experimental value of bandwidth, efficiency, resonant frequency, and beam pattern for several experimental models; and 3) the measurement of the effect of applied dc magnetic field.

Multiple-Post Inductive Obstacles in Rectangular Waveguide

A complete analysis of multiple-post inductive obstacles in rectangular waveguide is presented. A moment method solution with exponential ( e/sup jnTheta/) expansion and weighting functions is used in a Galerkin solution. Post currents are expressed as a Fourier series. As many Fourier series terms (e/sup jn Theta/) as desired may be included. All higher order (cutoff) mode interactions between posts are taken into account. The solution is rapid and accurate, and errors maybe controlled (specified). Data are given for the triple-post obstacle and for a two-element filter.

Near fields of wire antennas by matrix methods

The method of moments [1], [2] is applied to wire antenna near-field problems. Within the general method, two computational procedures are developed. Results of these are compared with those of certain approximate analytical techniques and also with those of other investigators. A treatment for junctions is outlined. Examples are included for a single dipole antenna, for linear arrays of dipoles and also for loop and T -junction radiators.

Analysis and Design of Wire Antennas with Applications to EMC

The method of moments is applied to wire antennas. Antenna analysis and beam pattern synthesis methods are outlined. Constraints appropriate to problems of EMC can readily be introduced. Some of the subjects treated are coupling, parasitic effects, pattern synthesis, null placement, and gain maximization. Numerous examples are given to illustrate the theory.

The response of a two-wire transmission line to incident field and voltage excitation, including the effects of higher order modes

The surface currents on a two-wire transmission line induced by incident field excitations are investigated using the spectral concept. A simple solution is obtained for plane wave excitation. A solution for voltage source excitation, in which the induced current may be given, at least approximately, by means of the so-called leaky-wave concept, is considered. The influence of the electrical dimensions of the structure on the currents and the relative importance of the higher modes are examined by numerical examples.

Dipole plus parasitic element

Some of the characteristics of a dipole plus a parallel parasitic element have been studied. The variation of resonant length as a function of parasitic spacing has been investigated using matrix inversion methods [1], [2] in conjunction with an iterative technique. Data on resonant resistance, beam patterns, and two-port open-circuit parameters are also given.

The Coupling of Electromagnetic Waves Through Long Slots

The problem of a plane wave incident upon one or more long, parallel slots in an infinite plane screen is treated by the method of moments. A Galerkins solution with triangular expansion and weighting functions is used. The complete solution for aperture fields, transmission coefficients, near and far fields is formulated and programmed. Arbitrary polarization and arbitrary angles of incidence are treated. Where comparison is possible, there is good agreement with classical results. Wide slots, and multiple slots, which cannot be treated by classical methods, are readily handled by the method of moments procedure. Two separate computer programs have been prepared for a) single slot and b) double slots. The theory is outlined; the computer program is described briefly, and representative examples are given.