D.A. McNamara

Analysis of radiating slots in a rectangular waveguide inhomogeneously loaded with a dielectric slab

Longitudinal and transverse radiating slots in the broad wall of a rectangular waveguide inhomogeneously loaded with a dielectric slab are analyzed. The formulation used involves the moment method solution of a pair of coupled integral equations containing the dyadic Greens function of the inhomogeneously loaded waveguide. Both an edge-condition for the electric field in the slot aperture and the correct form of the psi =constant waveguide mode are included in the analysis. Computed and measured results are compared to verify the theoretical analysis. >

A contoured beam synthesis technique for planar antenna arrays with quadrantal and centro-symmetry

A method is described for the synthesis of planar array antennas with prescribed contoured beams. The technique utilizes a transformation which divides the problem into two decoupled subproblems. One subproblem involves the determination of certain coefficients of the contour transformation in order to achieve the required footprint contours. The number of coefficients which need to be used depends on the complexity of the desired contour, but is very small in comparison to the number of planar array elements. The other subproblem consists of a linear array shaped beam synthesis, for which there already exist powerful methods for determining appropriate element excitations. The size required for this prototype linear array depends on the number of contour transformation coefficients used and the size of the final planar array. Simple formulas then determine the final planar array excitations from the information forthcoming from the above two subproblem solutions. >

Analysis of multiport discontinuities in waveguide using a pulsed FDTD approach

A pulsed finite-difference time-domain (FDTD) approach for computing the scattering parameters of multiport waveguide discontinuities and junctions is presented. Wideband absorbing boundary conditions (ABCs) necessary for implementation of the technique are derived. Applications of the technique are presented, and computed results are compared to measurements for several examples. >

On the functioning of folded dipole antennas on conducting masts

The radiation properties of individual folded dipole antennas mounted at various radial distances from the center of conducting masts of different diameters are described in a compact fashion. >

Experimental verification of an integral equation analysis of etched wire-grid antenna arrays

The application of an integral-equation moment method to the analysis of microstrip wire-grid antennas is discussed. The formulation has been implemented in computer code, which can be used to perform numerical experimentation. A coaxial-fed five-element etched linear array on a dielectric substrate is considered as an example. Such an analysis makes it possible to carefully design for some desired aperture distribution. Computed patterns are shown to compare favorably with measured results.<<ETX>>

Experimentally determined equivalent network scattering parameters for edge slots in rectangular waveguide for use as reference data

Tabulated, experimentally determined, scattering parameters for edge slots in the narrow wall of rectangular waveguide are given over a range of frequencies. The suggestion is that these tabulated results be used instead of graphs (extant in the literature since the 1940s) from which it is difficult accurately to read off slot properties for comparison with theoretical techniques which may be proffered in future work by others.<<ETX>>

The synthesis of difference patterns for planar arrays with rectangular and hexagonal lattices

The authors present a method of adapting linear array synthesis techniques appropriate for difference patterns so that they are applicable to the synthesis of planar arrays with difference patterns in a selected principal plane pattern cut. The sidelobes are all equal to or below those of the archetypal linear array, but not unnecessarily low, since this would cause an unwanted increase in the width of the difference pattern principal lobes. The technique in effect provides a structured procedure for spreading-out the linear array excitations, thereby eliminating any guesswork that may be required. The final planar array excitations are very simply related to the excitation coefficients of the archetypal linear array. This means that the technique can be used to rapidly synthesize even very large arrays. The difference pattern for a planar array with hexagonal boundary and lattice is considered as an illustrative result.<<ETX>>

An interactive computer-graphics-based processor for boundary element modelling of electromagnetic scattering by thin conducting wires

Abstract The method of moments, in the form of a boundary element method, has been widely applied to problems of electromagnetic scattering and radiation. The piecewise-sinusoid thin-wire antenna code developed by Richmond is reliable, efficient, and well-tested. This paper describes a personal-computer-based interactive pre- and post-processor code developed by the authors, which can be used to easily prepare data required for use with the Richmond code. All geometrical data is entered graphically, automatic segmentation of the structure is possible, datafiles can be stored for later use, existing datafiles (geometries) can be easily edited to create new geometries, and all numerical output data can be obtained in graphical form. The Richmond code is also included, for convenience, with the permission of its originator.