
Frank J. Villegas
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ABSTRACT: A parallel genetic algorithm (GA) optimization tool has been developed for the synthesis of arbitrarily shaped beam coverage using planar 2D phasedarray antennas. Typically, the synthesis of a contoured beam footprint using a planar 2D array is difficult because of the inherently large number of degrees of freedom involved (in general, the amplitude and phase of each element must be determined). We make use of a parallel GA tool in this study to compensate for this aspect of the design problem. The algorithm essentially compares a desired pattern envelope with that of trial arrays, and quantifies the effectiveness or desirability of each test case via a fitness function. The GA uses this information to rank and select subsequent arrays over a given number of generations via the conventional stochastic operators, i.e., selection, crossover, and mutation. Each fitness evaluation of a trial pattern is done on a node of the aerospace fellowship cluster supercomputer, which increases the speed of the algorithm linearly with the number of nodes. Because of the continuous nature of the parameters for this optimization problem, a real parameter encoding scheme is employed for the GA chromosome in order to avoid the quantization errors associated with a binary representation. A benchmark 10 times 10 (100) element array is employed, and various results of optimized coverage patterns are shown herein to illustrate the effectiveness and validity of the technique. No preview · Article · Jul 2007 · IEEE Transactions on Antennas and Propagation

Source Available from: Tom Cwik
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ABSTRACT: In this paper, we describe an electromagnetic genetic algorithm (GA) optimization (EGO) application developed for the cluster supercomputing platform. A representative patch antenna design example for commercial wireless applications is detailed, which illustrates the versatility and applicability of the method. We show that EGO allows us to combine the accuracy of fullwave EM analysis with the robustness of GA optimization and the speed of a parallel computing algorithm. A representative patch antenna design case study is presented. We illustrate the use of EGO to design a dualband antenna element for wireless communication (1.9 and 2.4 GHz) applications. The resulting antenna exhibits acceptable dualband operation (i.e., better than 10 dB return loss with 5.3 and 7% operating bandwidths at 1.9 and 2.4 GHz) while maintaining a crosspol maximum field level at least 11 dB below the copol maximum. Fulltext · Article · Oct 2004 · IEEE Transactions on Antennas and Propagation

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ABSTRACT: In this paper, we propose a novel hybrid space/spectraldomain methodofmoments (MoM) calculation of canonical planewave scattering from finite periodic structures comprised of dissimilar cylindrical cavities in an infinite ground plane, covered by a dielectric superstrate. We take full advantage of analyzing this particular type of problem (comprised of a canonical geometry) by employing a set of entiredomain basis functions (waveguide modes), which truly span the Hilbert space in which the desired solution resides. The convergence behavior of a solution using said functions is quite robust. Results show that typically only a few basis functions are required to adequately represent the aperture fields with fidelity. We have also reformulated the conventional magnetic field integral equation in a hybrid fashion, whereby the exterior (unbounded half space) MoM interaction terms have been cast in the spectral domain and the interior (cavity) interactions cast in the space domain directly. The spectral representation allows us to trivially include a superstrate layer in the geometry and additionally leads to an efficient evaluation of the interaction integrals due to an overall reduction in the spatial dimensionality. The interior interactions are readily handled in the space domain, where we take advantage of the orthogonality property of waveguide modes. Most importantly, the technique is significantly more accurate than purely numerical methods, i.e., those in which a discretization of the geometry is necessary. No preview · Article · Oct 2003 · IEEE Transactions on Antennas and Propagation

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ABSTRACT: In this paper, we investigate the scattering characteristics of finite onedimensional (1D) and twodimensional arrays of cylindrical cavities embedded within an infinite perfect electric conducting ground plane. Fundamental radar crosssection (RCS) features of said arrays are illustrated, with the RCS computed with respect to the scattered (diffracted) field component, obtained directly from the aperture currents. The aperture currents on the finite structure are computed using a hybrid space/spectraldomain MoM formulation. The complete set of (TE,TM) cylindrical eigenmodes are used to represent the unknowns. The dependence of the current distribution on the source polarization is shown for the canonical cavity. Threedimensional plots of the RCS signature of a 1D finite array illustrate the unique radiation characteristics of such structures, e.g., the constantdirectivity surfaces form cones about the array axis in 3D space. The effects of a superstrate layer on the radiation behavior of a 2D finite array are also shown. We find that the layer can in fact either enhance or diminish the radiation, depending on the source polarization. It also tends to reduce endfire radiation in all cases. The scattering signature of large finite arrays is computed approximately by the introduction of an active element factor defined specifically for scattering problems. Using the MoM solution of a reduced window array, we obtain the farfield patterns of larger structures by a simple computation of the array factor. An improvement to this approximation makes use of an exterior equivalent source, which models the localized edge effects. Finally, the use of nonuniform arrays for sidelobe suppression and 2D "masked" structures is illustrated. No preview · Article · Oct 2003 · IEEE Transactions on Antennas and Propagation

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ABSTRACT: The radiation field from a leaky mode on a semiinfinite printedcircuit line is investigated. Asymptotic formulas for the radiation field are presented for a mode that is either in the physical region (a fast wave with respect to the substrate mode into which leakage occurs), or in the spectralgap region (a slow wave). These formulas, as well as a numerically exact representation of the leakymode radiation field, are used to examine the nature of the radiation field and to study how it changes as the leaky mode transitions from the physical region to the spectralgap region. A comparison is made between the field radiated by the leakymode current and that radiated by a practical probe feed that launches the semiinfinite leaky mode current. Another comparison is made between the field radiated by the leakymode current and the exact field radiated by the total current that is excited by a practical gap voltage source on an infinite line. No preview · Article · Jun 2003

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ABSTRACT: In this paper, we make use of genetic algorithm (GA) optimization to arrive at an optimal (perhaps counterintuitive) design for a dualband patch antenna intended for wireless communication applications (operating at 1.9 and 2.4 GHz). To this end, we combine the accuracy of MoM fullwave solutions with the speed of parallel processing, and the robustness of the evolutionary optimization approach in an electromagnetic GA optimization application (EGO). The design (a descendant of the Epatch antenna), aims at achieving the goal of having an acceptable input VSWR while maintaining a low crosspolarized far field. To this end, an appropriate hybrid fitness function is employed in the GA. Field and S<sub>11</sub> measurements of various GAoptimized patch configurations exhibit good agreement with the MoM calculations. No preview · Conference Paper · Feb 2002

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ABSTRACT: We make use of a hybrid methodofmoments formulation for the
solution of scattering from finite, nonuniform, one and twodimensional
arrays of cylindrical cavities in an infinite ground plane. We show that
the method is rather versatile, with the capability to handle both small
and large finite arrays of dissimilar elements, including a dielectric
superstrate layer if desired. A modified AEF definition, specifically
developed for scattering type problems, has been employed to make the
analysis of very large arrays tenable. Scattering from novel
nonperiodic topologies is accommodated with the use of a 'masking'
procedure. We illustrate the overall versatility, accuracy and
efficiency of the method with a survey of various applications of
interest to the antenna and microwave engineering communities No preview · Conference Paper · Feb 2001

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ABSTRACT: We propose a new hybrid MoM formulation for the analysis of
scattering from dielectricallycovered finite arrays of cylindrical
cavities in an infinite ground plane, illuminated by a planewave
source. The new formulation focuses on the use of techniques that
maximize both the accuracy and efficiency of the numerical computations.
As a result, the algorithm is quite useful for analyzing rather large
yet finite structures without resorting to approximate methods. The
hybrid approach is both more accurate and efficient than purely
numerical solution techniques. Hence, the method has the additional
capacity to serve as a useful benchmarking application for other less
accurate numerical algorithms No preview · Conference Paper · Feb 2001

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ABSTRACT: We examined the scattering characteristics of a canonical rod/hole system. We found that the holes could simply be modeled as sections of cylindrical waveguides with shortcircuit terminations. Comparisons with fundamental quantities such as the guided wavelength and cutoff frequency yielded results that agreed quite well. The notion of an effective singlehole efficiency was introduced, implicitly accounting for interelement coupling. We found that it asymptotically tends to a constant value as the number of holes increases. We also concluded that the proximity of the rod to the grating plays an important role in the coupling phenomenon, a result of the travelingwave nature of the rod field. Finally, we compared a computed array farfield pattern with one based on a simple arrayfactor expression that includes an HFSS (a commercial 3D finiteelement EM simulator) computed leakage constant. The results lead to the conclusion that use of the effective efficiency as an array synthesis parameter will yield the predicted antenna characteristics No preview · Conference Paper · Feb 2000

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ABSTRACT: The radiation characteristics of a periodicallyloaded perfect electric conductor (PEC) circular cylinder fed by a proximitycoupled dielectric rod waveguide are investigated. The configuration, which is illustrated, is currently being employed as the core radiating mechanism in a host of millimeterwave (MMW) antenna systems for imaging and communications applications. Several rows of one dimensional gratings are placed along the cylinder axis, each with at slightly differing period, thus allowing for quasicontinuous scanning of the main beam in the Eplane of the antenna. For typical applications, precise control over the scanning behavior and overall radiation characteristics (e.g. beamwidth) is crucial, and as such an analysis tool capable of predicting the performance of the antenna would prove highly beneficial. To this end, we have developed an accurate, analytical formulation for the total radiated fields of the structure based on an eigenmode expansion. Using a cylindrical modal spectrum representation in which a fictitious axial leakywave current is impressed on the cylinder surface allows us to model the surface periodicity without the need for a timeconsuming fullwave analysis. Several salient features of the antenna's radiative properties concerning the various geometrical parameters involved are presented No preview · Conference Paper · Sep 1999

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ABSTRACT: The leakage fields radiated by planar semiinfinite
transmissionline currents are studied for two canonical structures: the
airgap stripline and the planar strip of current in free space. The
first structure represents a general class of printedcircuit structures
where leakage occurs into a substrate mode. The second structure is
representative of structures for which leakage occurs primarily into
space. It is found that the transverse behavior of the leakage fields
for a semiinfinite line differs in significant ways from that expected
from an infinite line, a result that is at first surprising, but is
understandable on physical grounds, and which is explained by the
analysis presented here. The exact leakage fields are compared with two
asymptotic approximations: a stationaryphase [geometrical optics (GO)]
evaluation, and a uniform asymptotic expansion (UAE). The UAE solution
is the more accurate one, and accounts for diffractionlike effects that
arise due to the semiinfinite nature of the line. One conclusion is
that the observation distance must be very large for the true leakage
fields to closely resemble the GO fields, although a quasiGO behavior
may still be evident at shorter distances, depending on the value of the
leakage angle. Another conclusion is that the transverse behavior of the
GO leakage field of the printedcircuit structure is an exponentially
increasing field within the leakage region, as expected from a simple
rayoptics picture, while it is not for the strip in free space No preview · Article · May 1999 · IEEE Transactions on Microwave Theory and Techniques

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ABSTRACT: A novel waveguidetomicrostrip transition is developed using a
new design methodology based on iris coupling. Key features of the
design are a singlelayer substrate, new matching topology, and new
cavity enclosure. The transition lends itself to a lowcost
implementation, while maintaining the enclosure's hermetic integrity. An
extensive tolerance study shows that the present design is robust and
very stable with respect to manufacturing and assembly variations.
Careful consideration has been given to the mechanical aspects of the
transition's implementation in order to achieve seamless integration
into the overall package manufacturing and assembly process without
sacrificing electrical performance. Proof of concept was achieved by
implementing a Qband (f<sub>0</sub>=44.5 GHz) design on alumina, a
Wband (f<sub>0</sub>=94 GHz) design on zcut quartz, and a Wband
design on fused silica. All exhibited better than 22 dB return loss at
their center frequencies with less than 0.3 dB insertion loss, and at
minimum a 10% 15 dB returnloss bandwidth No preview · Article · Feb 1999 · IEEE Transactions on Microwave Theory and Techniques

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ABSTRACT: The shapes of matching stubs are designed with an optimizer based
on fullwave analysis. By selecting the shape of matching stub as the
design parameter, compact circuits for matching could be obtained. FEM
is used as a fullwave analyzer, and adjoint variable method is adopted
for sensitivity analysis No preview · Conference Paper · Jan 1998

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ABSTRACT: A novel waveguide (w/g)tomicrostrip transition has been
developed using a new design methodology based on iris coupling. The
current design exhibits reduced sensitivity to w/g backshort position
and yields a lowcost, hermeticallysealed transition. A 44 GHzband
design on alumina and a 94 GHzband design on zcut quartz were
implemented, both exhibiting better than 22 dB return loss at their
center frequencies with less than 0.3 dB insertion loss, with a greater
than 10% bandwidth No preview · Conference Paper · Jul 1997

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ABSTRACT: The leakage fields radiated by planar semiinfinite transmission line currents are studied for two canonical structures, the airgap stripline and a strip in free space. The exact leakage fields are compared with the following two asymptotic approximations: a stationaryphase (geometrical optics or GO) evaluation and a uniform asymptotic expansion No preview · Conference Paper · Jul 1996