Matching Items (12)
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- All Subjects: Electromagnetism
- Genre: Doctoral Dissertation
- Creators: Aberle, James T., 1961-
- Creators: Balanis, Constantine A.
Description
Asymptotic and Numerical methods are popular in applied electromagnetism. In this work, the two methods are applied for collimated antennas and calibration targets, respectively. As an asymptotic method, the diffracted Gaussian beam approach (DGBA) is developed for design and simulation of collimated multi-reflector antenna systems, based upon Huygens principle and independent Gaussian beam expansion, referred to as the frames. To simulate a reflector antenna in hundreds to thousands of wavelength, it requires 1E7 - 1E9 independent Gaussian beams. To this end, high performance parallel computing is implemented, based on Message Passing Interface (MPI). The second part of the dissertation includes the plane wave scattering from a target consisting of doubly periodic array of sharp conducting circular cones by the magnetic field integral equation (MFIE) via Coiflet based Galerkin's procedure in conjunction with the Floquet theorem. Owing to the orthogonally, compact support, continuity and smoothness of the Coiflets, well-conditioned impedance matrices are obtained. Majority of the matrix entries are obtained in the spectral domain by one-point quadrature with high precision. For the oscillatory entries, spatial domain computation is applied, bypassing the slow convergence of the spectral summation of the non-damping propagating modes. The simulation results are compared with the solutions from an RWG-MLFMA based commercial software, FEKO, and excellent agreement is observed.
ContributorsWang, Le, 1975- (Author) / Pan, George (Thesis advisor) / Yu, Hongyu (Committee member) / Aberle, James T., 1961- (Committee member) / Diaz, Rodolfo (Committee member) / Kitchen, Jennifer (Committee member) / Arizona State University (Publisher)
Created2012
Description
When ferrite materials are used in antenna designs, they introduce some interesting and unique performance characteristics. One of the attractive features, for example, is the ability to reconfigure the center frequency of the antenna. In addition, ferrite materials also introduce a number of challenges in the modeling and simulation of such antennas. In order for the ferrite material to be useful in an antenna design, it usually is subjected to an external magnetic field. This field induces the internal magnetic field inside the ferrite material. The internal field plays a pivotal role in the radiation characteristics of the antenna. Thus, from the numerical point of view, accurate computation of this field is critical to the overall accuracy of the analysis. Usually the internal field is non-uniform and its computation is often a rather complex and non-trivial task. Therefore, to facilitate the modeling, simplifying assumptions, which introduce some kind of averaging, are often made. In this study, ferrite-loaded cavity-backed slot antennas are used to demonstrate that averaging procedures can lead to very unsatisfactory results. For instance, it is common practice to assume that the external field is uniform by averaging its distribution. One of the pivotal points in this study is the demonstration that the external magnetic field plays a very significant role and should be included in the modeling without averaging, if the accurate results are to be attained. Results presented in this study clearly support this argument. A procedure which avoids such averaging is presented and verified by comparing simulations with measurements. In contrast to the previous formulations, the modeling methodology developed in this dissertation leads to accurate results which compare very well with measurements for both uniform and non-uniform field distributions. The utility of this methodology is especially evident for the case when the magnetic field is severely non-uniform.
ContributorsKononov, Victor G (Author) / Balanis, Constantine A. (Thesis advisor) / Pan, George (Committee member) / Rajan, Subramaniam D. (Committee member) / Aberle, James T. (Committee member) / Arizona State University (Publisher)
Created2012
Description
Multiport antennas offer greater design flexibility than traditional one-port designs. An antenna array is a special case of a multiport antenna. If the antenna's inter-element spacing is electrically small, the antenna is capable of achieving superdirectivity. Superdirective antenna arrays are known to be narrow band and have low radiation resistance which leads to low radiation efficiency and high VSWR. However, by increasing the self-impedance of the antenna elements, the radiation resistance is increased but the bandwidth remains narrow. A design methodology is developed using the ability to superimpose electric fields and multi-objective optimization to design antenna feed networks. While the emphasis in this dissertation is on antenna arrays and superdirectivity, the design methodology is general and can be applied to other multiport antennas. The design methodology is used to design a multiport impedance-matching network and optimize both the input impedance and radiation pattern of a two-port superdirective antenna array. It is shown that the multiport impedance-matching network is capable of improving the input impedance of the antenna array while maintaining high directionality. The antenna design is critical for the methodology to improve the bandwidth and radiation characteristics of the array. To double the bandwidth of the two-port impedance matched superdirective antenna array, a three-port Yagi-Uda antenna design is demonstrated. The addition of the extra antenna element does not increase the footprint of the antenna array. The design methodology is then used to design a symmetrical antenna array capable of steering its main beam in two directions.
ContributorsArceo, Diana (Author) / Balanis, Constantine A (Thesis advisor) / Aberle, James T., 1961- (Committee member) / Moeller, Karl (Committee member) / Palais, Joseph (Committee member) / Arizona State University (Publisher)
Created2012
Description
There is a pervasive need in the defense industry for conformal, low-profile, efficient and broadband (HF-UHF) antennas. Broadband capabilities enable shared aperture multi-function radiators, while conformal antenna profiles minimize physical damage in army applications, reduce drag and weight penalties in airborne applications and reduce the visual and RF signatures of the communication node. This dissertation is concerned with a new class of antennas called Magneto-Dielectric wire antennas (MDWA) that provide an ideal solution to this ever-present and growing need. Magneto-dielectric structures (μr>1;εr>1) can partially guide electromagnetic waves and radiate them by leaking off the structure or by scattering from any discontinuities, much like a metal antenna of the same shape. They are attractive alternatives to conventional whip and blade antennas because they can be placed conformal to a metallic ground plane without any performance penalty. A two pronged approach is taken to analyze MDWAs. In the first, antenna circuit models are derived for the prototypical dipole and loop elements that include the effects of realistic dispersive magneto-dielectric materials of construction. A material selection law results, showing that: (a) The maximum attainable efficiency is determined by a single magnetic material parameter that we term the hesitivity: Closely related to Snoek's product, it measures the maximum magnetic conductivity of the material. (b) The maximum bandwidth is obtained by placing the highest amount of μ" loss in the frequency range of operation. As a result, high radiation efficiency antennas can be obtained not only from the conventional low loss (low μ") materials but also with highly lossy materials (tan(δm)>>1). The second approach used to analyze MDWAs is through solving the Green function problem of the infinite magneto-dielectric cylinder fed by a current loop. This solution sheds light on the leaky and guided waves supported by the magneto-dielectric structure and leads to useful design rules connecting the permeability of the material to the cross sectional area of the antenna in relation to the desired frequency of operation. The Green function problem of the permeable prolate spheroidal antenna is also solved as a good approximation to a finite cylinder.
ContributorsSebastian, Tom (Author) / Diaz, Rodolfo E (Thesis advisor) / Pan, George (Committee member) / Aberle, James T., 1961- (Committee member) / Kozicki, Michael (Committee member) / Arizona State University (Publisher)
Created2013
Description
A domain decomposition method for analyzing very large FDTD domains, hundreds of thousands of wavelengths long, is demonstrated by application to the problem of radar scattering in the maritime environment. Success depends on the elimination of artificial scattering from the “sky” boundary and is ensured by an ultra-high-performance absorbing termination which eliminates this reflection at angles of incidence as shallow as 0.03 degrees off grazing. The two-dimensional (2D) problem is used to detail the features of the method. The results are cross-validated by comparison to a parabolic equation (PE) method and surface integral equation method on a 1.7km sea surface problem, and to a PE method on propagation through an inhomogeneous atmosphere in a 4km-long space, both at X-band. Additional comparisons are made against boundary integral equation and PE methods from the literature in a 3.6km space containing an inhomogeneous atmosphere above a flat sea at S-band. The applicability of the method to the three-dimensional (3D) problem is shown via comparison of a 2D solution to the 3D solution of a corridor of sea. As a technical proof of the scalability of the problem with computational power, a 5m-wide, 2m-tall, 1050m-long 3D corridor containing 321.8 billion FDTD cells has been simulated at X-band. A plane wave spectrum analysis of the (X-band) scattered fields produced by a 5m-wide, 225m-long realistic 3D sea surface, and the 2D analog surface obtained by extruding a 2D sea along the width of the corridor, reveals the existence of out-of-plane 3D phenomena missed by the traditional 2D analysis. The realistic sea introduces random strong flashes and nulls in addition to a significant amount of cross-polarized field. Spatial integration using a dispersion-corrected Green function is used to reconstruct the scattered fields outside of the computational FDTD space which would impinge on a 3D target at the end of the corridor. The proposed final approach is a hybrid method where 2D FDTD carries the signal for the first tens of kilometers and the last kilometer is analyzed in 3D.
ContributorsDowd, Brandon (Author) / Diaz, Rodolfo E (Thesis advisor) / Pan, George (Committee member) / Schmidt, Kevin (Committee member) / Aberle, James T., 1961- (Committee member) / Arizona State University (Publisher)
Created2018
Description
We present fast and robust numerical algorithms for 3-D scattering from perfectly electrical conducting (PEC) and dielectric random rough surfaces in microwave remote sensing. The Coifman wavelets or Coiflets are employed to implement Galerkin’s procedure in the method of moments (MoM). Due to the high-precision one-point quadrature, the Coiflets yield fast evaluations of the most off-diagonal entries, reducing the matrix fill effort from O(N^2) to O(N). The orthogonality and Riesz basis of the Coiflets generate well conditioned impedance matrix, with rapid convergence for the conjugate gradient solver. The resulting impedance matrix is further sparsified by the matrix-formed standard fast wavelet transform (SFWT). By properly selecting multiresolution levels of the total transformation matrix, the solution precision can be enhanced while matrix sparsity and memory consumption have not been noticeably sacrificed. The unified fast scattering algorithm for dielectric random rough surfaces can asymptotically reduce to the PEC case when the loss tangent grows extremely large. Numerical results demonstrate that the reduced PEC model does not suffer from ill-posed problems. Compared with previous publications and laboratory measurements, good agreement is observed.
ContributorsZhang, Lisha (Author) / Pan, George (Thesis advisor) / Diaz, Rodolfo (Committee member) / Aberle, James T., 1961- (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2016
Description
Articially engineered two-dimensional materials, which are widely known as
metasurfaces, are employed as ground planes in various antenna applications. Due to
their nature to exhibit desirable electromagnetic behavior, they are also used to design
waveguiding structures, absorbers, frequency selective surfaces, angular-independent
surfaces, etc. Metasurfaces usually consist of electrically small conductive planar
patches arranged in a periodic array on a dielectric covered ground plane. Holographic
Articial Impedance Surfaces (HAISs) are one such metasurfaces that are capable of
forming a pencil beam in a desired direction, when excited with surface waves. HAISs
are inhomogeneous surfaces that are designed by modulating its surface impedance.
This surface impedance modulation creates a periodical discontinuity that enables a
part of the surface waves to leak out into the free space leading to far-eld radia-
tion. The surface impedance modulation is based on the holographic principle. This
dissertation is concentrated on designing HAISs with
Desired polarization for the pencil beam
Enhanced bandwidth
Frequency scanning
Conformity to curved surfaces
HAIS designs considered in this work include both one and two dimensional mod-
ulations. All the designs and analyses are supported by mathematical models and
HFSS simulations.
metasurfaces, are employed as ground planes in various antenna applications. Due to
their nature to exhibit desirable electromagnetic behavior, they are also used to design
waveguiding structures, absorbers, frequency selective surfaces, angular-independent
surfaces, etc. Metasurfaces usually consist of electrically small conductive planar
patches arranged in a periodic array on a dielectric covered ground plane. Holographic
Articial Impedance Surfaces (HAISs) are one such metasurfaces that are capable of
forming a pencil beam in a desired direction, when excited with surface waves. HAISs
are inhomogeneous surfaces that are designed by modulating its surface impedance.
This surface impedance modulation creates a periodical discontinuity that enables a
part of the surface waves to leak out into the free space leading to far-eld radia-
tion. The surface impedance modulation is based on the holographic principle. This
dissertation is concentrated on designing HAISs with
Desired polarization for the pencil beam
Enhanced bandwidth
Frequency scanning
Conformity to curved surfaces
HAIS designs considered in this work include both one and two dimensional mod-
ulations. All the designs and analyses are supported by mathematical models and
HFSS simulations.
ContributorsPandi, Sivaseetharaman (Author) / Balanis, Constantine A (Thesis advisor) / Palais, Joseph (Committee member) / Aberle, James T., 1961- (Committee member) / Trichopoulos, Georgios (Committee member) / Arizona State University (Publisher)
Created2017
Description
Impedance-modulated metasurfaces are compact artificially-engineered surfaces whose surface-impedance profile is modulated with a periodic function. These metasurfaces function as leaky-wave antennas (LWAs) that are capable of achieving high gains and narrow beamwidths with thin and light-weight structures. The surface-impedance modulation function for the desired radiation characteristics can be obtained using the holographic principle, whose application in antennas has been investigated extensively.
On account of their radiation and physical characteristics, modulated metasurfaces can be employed in automotive radar, 5G, and imaging applications. Automotive radar applications might require the antennas to be flush-mounted on the vehicular bodies that can be curved. Hence, it is necessary to analyze and design conformal metasurface antennas. The surface-impedance modulation function is derived for cylindrically-curved metasurfaces, where the impedance modulation is along the cylinder axis. These metasurface antennas are referred to as axially-modulated cylindrical metasurface LWAs (AMCLWAs). The effect of curvature is modeled, the radiation characteristics are predicted analytically, and they are validated by simulations and measurements.
Communication-based applications, like 5G and 6G, require the generation of multiple beams with polarization diversity, which can be achieved using a class of impedance-modulated metasurfaces referred to as polarization-diverse holographic metasurfaces (PDHMs). PDHMs can form, one at a time, a pencil beam in the desired direction with horizontal polarization, vertical polarization, left-hand circular polarization (LHCP), or right-hand circular polarization (RHCP). These metasurface antennas are analyzed, designed, measured, and improved to include the ability to frequency scan.
In automotive radar and other imaging applications, the performance of metasurface antennas can be impacted by the formation of standing waves due to multiple reflections between the antenna and the target. The monostatic RCS of the metasurface antenna is reduced by modulating its surface impedance with a square wave, to avert multiple reflections. These square-wave-modulated metasurfaces are referred to as checkerboard metasurface LWAs, whose radiation and scattering characteristics, for normal incidence parallel polarization, are analyzed and measured.
On account of their radiation and physical characteristics, modulated metasurfaces can be employed in automotive radar, 5G, and imaging applications. Automotive radar applications might require the antennas to be flush-mounted on the vehicular bodies that can be curved. Hence, it is necessary to analyze and design conformal metasurface antennas. The surface-impedance modulation function is derived for cylindrically-curved metasurfaces, where the impedance modulation is along the cylinder axis. These metasurface antennas are referred to as axially-modulated cylindrical metasurface LWAs (AMCLWAs). The effect of curvature is modeled, the radiation characteristics are predicted analytically, and they are validated by simulations and measurements.
Communication-based applications, like 5G and 6G, require the generation of multiple beams with polarization diversity, which can be achieved using a class of impedance-modulated metasurfaces referred to as polarization-diverse holographic metasurfaces (PDHMs). PDHMs can form, one at a time, a pencil beam in the desired direction with horizontal polarization, vertical polarization, left-hand circular polarization (LHCP), or right-hand circular polarization (RHCP). These metasurface antennas are analyzed, designed, measured, and improved to include the ability to frequency scan.
In automotive radar and other imaging applications, the performance of metasurface antennas can be impacted by the formation of standing waves due to multiple reflections between the antenna and the target. The monostatic RCS of the metasurface antenna is reduced by modulating its surface impedance with a square wave, to avert multiple reflections. These square-wave-modulated metasurfaces are referred to as checkerboard metasurface LWAs, whose radiation and scattering characteristics, for normal incidence parallel polarization, are analyzed and measured.
ContributorsRamalingam, Subramanian (Author) / Balanis, Constantine A. (Thesis advisor) / Aberle, James T. (Committee member) / Palais, Joseph C. (Committee member) / Trichopoulos, Georgios C. (Committee member) / Arizona State University (Publisher)
Created2020
Description
Presented is a design approach and test of a novel compact waveguide that demonstrated the outer dimensions of a rectangular waveguide through the introduction of parallel raised strips, or flanges, which run the length of the rectangular waveguide along the direction of wave propagation. A 10GHz waveguide was created with outer dimensions of a=9.0mm and b=3.6mm compared to a WR-90 rectangular waveguide with outer dimensions of a=22.86mm and b=10.16mm which the area is over 7 times the area. The first operating bandwidth for a hollow waveguide of dimensions a=9.0mm and b=3.6mm starts at 16.6GHz a 40% reduction in cutoff frequency.
The prototyped and tested compact waveguide demonstrated an operating close to the predicted 2GHz with predicted vs measured injection loss generally within 0.25dB and an overall measured injection loss of approximately 4.67dB/m within the operating bandwidth.
The prototyped and tested compact waveguide demonstrated an operating close to the predicted 2GHz with predicted vs measured injection loss generally within 0.25dB and an overall measured injection loss of approximately 4.67dB/m within the operating bandwidth.
ContributorsJones, Jimmy, Ph.D (Author) / Pan, George (Thesis advisor) / Palais, Joseph (Committee member) / Aberle, James T., 1961- (Committee member) / Young, William (Committee member) / Arizona State University (Publisher)
Created2019
Description
Within the past two decades, metasurfaces, with their unique ability to tailor the wavefront, have attracted scientific attention. Along with many other research areas, RADAR cross-section (RCS)-reduction techniques have also benefited from metasurface technology.
In this dissertation, a novel technique to synthesize the RCS-reduction metasurfaces is presented. This technique unifies the two most widely studied and two well-established modern RCS-reduction methods: checkerboard RCS-reduction andgradient-index RCS-reduction. It also overcomes the limitations associated with these RCS-reduction methods. It synthesizes the RCS-reduction metasurfaces, which can be juxtaposed with almost any existing metasurface, to reduce its RCS. The proposed technique is fundamentally based on scattering cancellation. Finally, an example of the RCS-reduction metasurface has been synthesized and introduced to reduce the RCS of an existing high-gain metasurface ground plane.
After that, various ways of obtaining ultrabroadband RCS-reduction using the same technique are proposed, which overcome the fundamental limitation of the conventional checkerboard metasurfaces, where the reflection phase difference of (180+-37) degrees is required to achieve 10-dB RCS reduction. First, the guideline on how to select Artificial Magnetic Conductors (AMCs) is explained with an example of a blended checkerboard architecture where a 10-dB RCS reduction is observed over 83% of the bandwidth. Further, by modifying the architecture of the blended checkerboard metasurface, the 10-dB RCS reduction bandwidth increased to 91% fractional bandwidth. All the proposed architectures are validated using measured data for fabricated prototypes. Critical steps for designing the ultrabroadband RCS reduction checkerboard surface are summarized.
Finally, a broadband technique to reduce the RCS of complex targets is presented. By using the proposed technique, the problem of reducing the RCS contribution from such multiple-bounces simplifies to identifying and implementing a set of orthogonal functions. Robust guidelines for avoiding grating lobes are provided using array theory. The 90 degree dihedral corner is used to verify the proposed technique. Measurements are reported for a fabricated prototype, where a 70% RCS-reduction bandwidth is observed. To generalize the method, a 45 degree dihedral corner, with a quadruple-bounce mechanism, is considered. Generalized guidelines are summarized and applied to reduce the RCS of complex targets using the proposed method.
In this dissertation, a novel technique to synthesize the RCS-reduction metasurfaces is presented. This technique unifies the two most widely studied and two well-established modern RCS-reduction methods: checkerboard RCS-reduction andgradient-index RCS-reduction. It also overcomes the limitations associated with these RCS-reduction methods. It synthesizes the RCS-reduction metasurfaces, which can be juxtaposed with almost any existing metasurface, to reduce its RCS. The proposed technique is fundamentally based on scattering cancellation. Finally, an example of the RCS-reduction metasurface has been synthesized and introduced to reduce the RCS of an existing high-gain metasurface ground plane.
After that, various ways of obtaining ultrabroadband RCS-reduction using the same technique are proposed, which overcome the fundamental limitation of the conventional checkerboard metasurfaces, where the reflection phase difference of (180+-37) degrees is required to achieve 10-dB RCS reduction. First, the guideline on how to select Artificial Magnetic Conductors (AMCs) is explained with an example of a blended checkerboard architecture where a 10-dB RCS reduction is observed over 83% of the bandwidth. Further, by modifying the architecture of the blended checkerboard metasurface, the 10-dB RCS reduction bandwidth increased to 91% fractional bandwidth. All the proposed architectures are validated using measured data for fabricated prototypes. Critical steps for designing the ultrabroadband RCS reduction checkerboard surface are summarized.
Finally, a broadband technique to reduce the RCS of complex targets is presented. By using the proposed technique, the problem of reducing the RCS contribution from such multiple-bounces simplifies to identifying and implementing a set of orthogonal functions. Robust guidelines for avoiding grating lobes are provided using array theory. The 90 degree dihedral corner is used to verify the proposed technique. Measurements are reported for a fabricated prototype, where a 70% RCS-reduction bandwidth is observed. To generalize the method, a 45 degree dihedral corner, with a quadruple-bounce mechanism, is considered. Generalized guidelines are summarized and applied to reduce the RCS of complex targets using the proposed method.
ContributorsModi, Anuj (Author) / Balanis, Constantine A. (Thesis advisor) / Palais, Joseph C. (Committee member) / Aberle, James T. (Committee member) / Trichopoulos, Georgios C. (Committee member) / Arizona State University (Publisher)
Created2020