Sembiam R. Rengarajan

Genetic algorithms in the design and optimization of antenna array patterns

This paper demonstrates the application of genetic algorithms (GAs) in array pattern synthesis. GAs have the ability to escape from local minima and maxima and are ideally suited for problems where the number of variables is very high. We present three examples: two for linear arrays and one involving linear and planar arrays.

Compound radiating slots in a broad wall of a rectangular waveguide

An analysis is presented of the characteristics of a broad wall radiating slot, offset from the center line and tilted with respect to the longitudinal axis of a rectangular waveguide. Pertinent integral equations are developed, taking into account finite wall thickness, and are solved for the slot aperture E-field using the method of moments. Compound slot characteristics are then deduced, including resonant length and dominant mode scattering. Numerical results for the scattering from resonant slots are presented over a range of offsets, tilt angles, frequencies and waveguide dimensions. For resonant compound slots, offset and tilt are shown to control the aperture electric-field amplitude with a phase variability of 360 degrees . The results have significant applications in the design of compound slot arrays. >

Analysis of a centered-inclined waveguide slot coupler

Integral equations are developed for a centered-inclined coupling slot (including the effect of finite wall-thickness of the common broad-wall) and the slot-aperture electric intensity field is found using the method of moments. Numerical results for resonant length, backscattered wave amplitude, and phase variation off-resonance are presented over a range of values of the waveguide b dimension, wall thickness, slot width, and frequency. It is shown that the resonant length is relatively insensitive to slot tilt, theta , for a standard-height X-band waveguide, whereas its dependence on theta is significant for reduced-height waveguides. The phase variation of scattered TE/sub 10/ waves in both waveguides off-resonance is less for wider slots and smaller b dimensions. Shunt-series coupling slots exhibit greater phase variation off resonance when compared to a centred-inclined coupling slot. Also, the former has a longer resonant length for a smaller b dimension and for a wider slot. Thus the centred-inclined slot coupler possesses superior characteristics. The higher-order mode coupling between a centred-inclined slot coupler and a pair of straddling radiating slots in the branch waveguide is significant. >

The field equivalence principle: illustration of the establishment of the non-intuitive null fields

The field equivalence principle, one of the fundamental concepts in electromagnetics, has numerous applications. However, for a beginning student, it is not easy to understand this concept thoroughly and to appreciate it. The dilemma faced by beginning students is illustrated. We have sources in a finite Region I, and an arbitrary mathematical surface separating Regions I and II. The equivalent problems for the exterior and interior regions are specified with the use of electric and magnetic equivalent currents impressed on the boundary surface. The acceptance of the establishment by the equivalent sources of the non-intuitive null field for the exterior problem (by the equivalent sources and the original source for the interior problem) is commonly bothersome and not comfortably realized. In order to clarify this, we revisit Loves and Schelkunoff s forms of the equivalence principle. Subsequently, we discuss two simple, analytically tractable illustrative examples, consisting of plane-wave fields in two half-space regions, separated by an infinite planar surface. In particular, the emphasis is on the establishment of the non-intuitive null fields developed by these equivalent sources. Various forms of equivalence are illustrated by simple analytical field expressions.

Analysis of nearly cylindrical antennas and scattering problems using a spectrum of two-dimensional solutions

This paper presents a powerful method to analyzeantennas which can be considered principally two-dimensional(2-D) or cylindrical, except for some three-dimensional (3-D)physical or equivalent sources, e.g., dipoles or slots. It is shown byFourier transform techniques that such antennas can be analyzedas 2-D problems with harmonic longitudinal field variation. Theradiation pattern can often be determined directly from a finiteset of such 2-D solutions, each one obtained by any method, e.g.,the moment method. The mutual interaction between the cylindrical scatterer and the sources must be calculated to determine theexact current distribution on the sources and their impedances oradmittances. This is facilitated by performing an inverse Fouriertransform of an infinite spectrum of the numerical 2-D solutionsfollowed by a moment method solution in the spatial domain tosatisfy the boundary conditions on the 3-D equivalent sourcesthemselves. The inverse Fourier transform is simplified by theuse of asymptote extraction. The method is in itself a hybridtechnique as one method is used to solve the harmonic 2-Dproblem, and the other to solve for the source currents

Admittance of an isolated waveguide-fed slot radiating between baffles using a spectrum of two-dimensional solutions

An efficient method of computing resonant length and admittance characteristics of an isolated broad-wall shunt slot radiating between baffles of finite height is presented. The outer three-dimensional (3D) field problem associated with this geometry is reduced to a two-dimensional (2D) one via a Fourier transformation with respect to the longitudinal z direction. For each value of the longitudinal wave number k/sub z/ an integral equation is solved for the E field in the mouth of the plates using the method of moments. This procedure is repeated for several discrete values of k/sub z/, to obtain a spectrum of 2D solutions which are then inverse-transformed to construct the 3D solution in the spatial domain for the exterior baffle region and the half space. The slot aperture field is determined by the conventional moment method solution to the integral equation that enforces the continuity of the H field across the slot. Scattering properties of the slot are then deduced. Numerical results for the resonant length and resonant conductance are presented. Computer results are found to be in good agreement with experimentally measured data. >

Antenna Engineering Using Physical Optics

This book sets itself the rather ambitious task of providing programs in three languages. It does not limit itself to the FORTRAN language, which has traditionally been the workhorse of most scientific and engineering software-development efforts, and is routinely used by engineers. The C language and its variations, such as C++, are very popular these days. One of the strengths of this book is that it shows the feasibility of the application of the MATLAB language to antenna field problems using the physical-optics approach, which makes it also a nice and useful introduction to the physical-optics method in electromagnetics. The book uses the term physical optics loosely to denote all methods of finding radiated fields via a process of integration of approximate equivalent currents with appropriate Greens functions.

Characteristics of a longitudinal/transverse coupling slot in crossed rectangular waveguides

A rigorous analysis of a broad-wall slot coupler between two crossed rectangular waveguides is presented. The slot is longitudinal and offset from the center line in the main guide and is centered transverse in the branch guide. Integral equations are developed, taking into account finite wall thickness. The integral equations are then solved for the aperture electric field. Coupling slot characteristics are obtained, including the resonant length and dominant mode scattering. Numerical results for resonant length and scattering parameters are presented over a range of offsets, waveguide dimensions, and frequencies. >

Accurate characterization of coupling junctions in waveguide-fed planar slot arrays

This paper presents a rigorous analysis of coupling junctions employed in waveguide-fed planar slot arrays consisting of a main waveguide and a family of crossed branch waveguides wherein radiating slots are cut. Each coupling junction typically consists of a centered-inclined coupling slot in the common broad wall of two orthogonal waveguides and a pair of straddling longitudinal radiating slots located a quarter guide wavelength away in the branch waveguide. In the prior literature, only the dominant mode coupling between the coupling and radiating slots has been considered. In this analysis, coupling through all higher order modes in the junction region, including the singularity in the coupling problem, have been accounted for. Waveguide Greens functions in k/sub z/-spectral form have been found to be convenient for this analysis. Numerical results on higher-order mode coupling effects in coupling junctions are presented over a wide range of waveguide and slot parameters. The theoretical model discussed in this paper has been validated with experiments. Results presented here should find applications in the analysis and synthesis of planar slot arrays. >

Optimal compromise among sum and difference patterns

Three methods to obtain compromised sets of excitations in monopulse antenna arrays are investigated. The techniques involve minimizing a scalar-valued performance measure, called cost function, via the use of simulated annealing method. The unknowns in the cost function are the weight factors of each sub-array or the relative amplitudes and the phases of the excitations of the array elements. Several examples are presented to illustrate the optimal results obtained.