Showing papers in "Electromagnetics in 2000"
TL;DR: The spiral is treated as a traveling-wave structure that has unique ultra-broadband, complex, multi-facet radiation characteristics, and development of spirals with efficient transmit performance suitable for all applications such as telecommunications and radar are reported.
Abstract: The spiral has been limited to applications for receive only because it is invariably loaded dissipatively, with a typical 3-dB loss and the resulting low efficiency. In this article, we treat the spiral as a traveling-wave (TW) structure that has unique ultra-broadband, complex, multi-facet radiation characteristics, and report development of spirals with efficient transmit performance suitable for all applications such as telecommunications and radar. Its excellent form factor and its size reduction potential are discussed. The spiral's unique geometry is also shown to allow easy and powerful switching, control and various manipulations, etc., to achieve performance and special features that are difficult or even impossible by antennas of other geometries. These unique multimode, multi-polarization, and inherent phase patterns are utilized to achieve ultra-broadband phased arrays and smart antennas for applications involving multifunction, real-time switched modes, among others.
52 citations
TL;DR: A new method for calculating the resonant resistance of electrically thin and thick rectangular microstrip patch antennas, based on the artificial neural networks, is presented.
Abstract: A new method for calculating the resonant resistance of electrically thin and thick rectangular microstrip patch antennas, based on the artificial neural networks, is presented. The four learning algorithms, the backpropagation, the delta-bar-delta, the quick propagation, and the extended-delta-bar-delta, are used to train the networks. The theoretical resonant resistance results obtained by using this method are in very good agreement with the experimental results available in the literature.
45 citations
TL;DR: The perfectly matched layer is a successful concept used in finite difference numerical techniques as discussed by the authors, and it can be also considered as a uniaxial medium whose tensor material parameters are subject to certain requirements.
Abstract: The perfectly matched layer is a successful concept used in finite difference numerical techniques. It can be also considered as a uniaxial medium whose tensor material parameters are subject to certain requirements. Here we demonstrate that such a medium is in principle physically realizable as a composite material with small inclusions, but the inclusions must be active, which means that they can only be realized as active electronic circuits, e.g., circuits based on operational amplifiers.
21 citations
TL;DR: In this paper, a new type of spiral antenna utilizing slot radiating elements is presented that eliminates these drawbacks, relying instead on several new approaches to guarantee its frequency-independent operation over extremely broad bandwidths.
Abstract: Previously, the broadband spiral class of antennas primarily consisted of the wire (or "printed")spiral and spirals with approximately complementary geometry. While both are very broadband radiators, they are still somewhat band-limited due to their associated balun structures, and bulky as a result of their absorbing cavities. A new type of spiral antenna utilizing slot radiating elements is presented that eliminates these drawbacks, relying instead on several new approaches to guarantee its frequency-independent operation over extremely broad bandwidths. The design and integration of a planar infinite balun/feed structure and very shallow reflecting cavity is presented and discussed, as is a new termination technique. Gain, axial ratio, and pattern measurements for both a 6" (15.24 cm)diameter spiral, with flow = 750 M Hz and 6.25:1 bandwidth, and an 18" (45.72lcm) diameter spiral, with flow = 250 M Hz and 15:1 bandwidth, are also given and reviewed.
17 citations
TL;DR: In this article, a general 3D interpolation model is developed to select M vertical planes (perpendicular to the interfaces of the multilayered medium) to be tabulated in an overlapping manner to interpolate between them.
Abstract: Analysis of arbitrarily shaped three-dimensional (3D) objects in a multilayered medium using the method of moments (MoM) requires the computation of the Green's functions. When MoM is applied in the spatial domain, a 3D integral (one for the Sommerfeld integral, the other two for the integral over the source triangle) should be evaluated. The evaluation of the Sommerfeld integrals is a time-consuming process. A commonly encountered solution for this problem is to perform interpolations using preestablished look-up tables. Here, a general 3D interpolation model has been developed. The interpolation scheme is to select M vertical planes (perpendicular to the interfaces of the multilayered medium) to be tabulated in an overlapping manner to interpolate between them. In this scheme, all the grid values on the same vertical plane are tabulated and a single subroutine call is required to evaluate the Green's function. The interpolation model has been employed to calculate the current distributions on a TE 01del...
17 citations
TL;DR: In this article, the authors implemented the Floquet theorem in finite difference time domain (FDTD) for the analysis of periodic phased array antennas, where the array grid of interest is considered to be generally skewed.
Abstract: The Floquet (periodic) theorem is implemented in finite difference time domain (FDTD) for the analysis of periodic phased array antennas. The array grid of interest is considered to be generally skewed and this required a new procedure in the implementation of the Floquet theorem in FDTD. Numerical results for triangular antenna arrays are given to validate the proposed method of solution.
14 citations
TL;DR: In this paper, the axial ratio and array gain enhancements in an off-axis coverage zone were investigated numerically and experimental prototypes were implemented and tested over a finite 4.5k 3 4 5k ground plane.
Abstract: The curl antenna is a single-turn horizontal spiral fed by a monopole-like feed. The spiral and monopole dimensions are usually optimized to improve its radiation field and axial ratio for broadside radiation. It is shown in this study that the axial ratio can be optimized in certain regions of the radiation zone. In addition, the radiation pattern can be tilted off its axis on one side, which may be used to improve the array pattern scanning in small arrays. The concept is used for design of small planar arrays for mobile satellite communications. The axial ratio and array gain enhancements, in an off-axis coverage zone, are initially investigated numerically. The array is placed over an infinite ground plane. Experimental prototypes are, however, implemented and tested over a finite 4.5k 3 4.5k ground plane. The axial ratio performance appears to remain satisfactory, but the array gain reduces slightly, due to the back radiation. The curl antenna configuration, in dual inverted form, is also used for wide-angle axial ratio improvement. It provides a compact high-gain antenna with excellent circular polarization over most of the hemispherical region.
12 citations
TL;DR: The physical theory of diffraction with transition currents (PTD-TC) is used to predict the electromagnetic fields diffracted by obstacles with or without edges, and its usefulness is verified by applying it to perfectly conducting rectangular and ogive cylinders as discussed by the authors.
Abstract: The physical theory of diffraction with transition currents (PTD-TC) is used to predict the electromagnetic fields diffracted by obstacles with or without edges, and its usefulness is verified by applying it to perfectly conducting rectangular and ogive cylinders. Edge and transition currents are borrowed from the solution of canonical problems of wedge and circular cylinders. Transition currents of curved surfaces are represented in the form of the Fock-type integral. For an obstacle with edges, the currents near the edges are expressed by eigenfunction expansion. The currents of other parts are represented by the Fresnel integral, which has a slightly different form than that derived by Kouyoumjian and Pathak. Numerical results of far-scattered patterns are obtained and compared with those obtained by the method of moments. It was found that the present method gives very precise results.
9 citations
TL;DR: In this paper, an exact general expression of dyadic Green's function (DGF) for the problem of electromagnetic radiation from a source of excitation in the presence of a layered spherical dielectric head model, which is valid everywhere, including the source region.
Abstract: The principle objectives of our research are twofold. We outline an exact general expression of dyadic Green's function (DGF) for the problem of electromagnetic radiation from a source of excitation in the presence of a layered spherical dielectric head model, which is valid everywhere, including the source region. The medium is assumed to be homogeneous, isotropic, linear, nondispersive, and stationary. The DGFs are obtained by employing the method of scattering superposition. Second, a compact alternative general representation is developed to determine the electric- and magnetic-type DGFs, giving clarity as well as more efficient and economical computation in terms of speed, time, and memory.
9 citations
TL;DR: In this article, the conditions for maximum directivity and minimum reflection loss for elliptical and hyperhemispherical synthesized lenses are investigated. And the results are confirmed experimentally.
Abstract: Typical limitations of integrated antennas such as bidirectional radiation, power loss via substrate modes, and broad radiation patterns can be corrected using a substrate lens. In this paper, various slot-fed substrate lens antenna (SLA) configurations are examined, and a novel hybrid physical optics analysis technique, suitable for electrically small geometries, is presented. Based on this method, directivity and reflection loss calculations for elliptical and hyperhemispherical synthesized lenses are carried out. It is found that the conditions for maximum directivity and minimum reflection loss do not coincide, and thus certain performance compromises are necessary. The results are confirmed experimentally.
9 citations
TL;DR: In this paper, two types of structures with uniaxial magnetic anistropy in each layer are proposed for absorption of electromagnetic waves by thin multilayer magnetogyrotropic structures.
Abstract: This article treats absorption of electromagnetic waves by thin multilayer magnetogyrotropic structures. Two types of structures with uniaxial magnetic anistropy in each layer are proposed. In structure I, easy magnetization axes in layers are normal to the layers plane. In structure II, easy magnetization axes are parallel to one of the coordinate axes, lying in the layers plane. Structure I is made as glass-fiber-reinforced plastic, with each layer containing a set of tiles, made from textured hexaferrites. This structure can also be made from multilayer fabrics of ultrahigh molecular weight polyethylene fibers, filled with magnetically uniaxial hexaferrites, having natural ferromagnetic resonance frequencies from 14 to 40 GHz. Structure II is made as multilayer fabrics from ultrahigh molecular weight polyethylene fibers, filled with hexaferrites, having a plane or cone of magnetization and natural ferromagnetic resonance frequencies 1 to 20 GHz.
TL;DR: In this article, a full-wave three-dimensional integral-equation moment method is used to find the propagation constants of guided-wave modes on grounded dielectric slabs with planar artificial periodic implants.
Abstract: Surface-wave (or dielectric slab) modes in integrated circuit structures often result in undesired energy losses and cross-talk between components. In this paper, surface-wave elimination in integrated circuit structures by using planar artificial periodic substrates is investigated. A full-wave three-dimensional integral-equation moment-method is used to find the propagation constants of guided-wave modes on grounded dielectric slabs with planar periodic implants. The cases of rectangular blocks in both a rectangular lattice and a triangular lattice are investigated. The limitation on complete (omnidirectional) surface-wave elimination with material grating is discussed. This work may lead to the development of many novel integrated circuit components with potential significance in millimeter waves and optics.
TL;DR: In this article, an N-spiral array antenna mounted on a finite-length conducting cylinder of length 2L yc and radius rcy is numerically analyzed using the method of moments (MoM).
Abstract: An N-spiral array antenna mounted on a finite-length conducting cylinder of length 2L yc and radius rcy is numerically analyzed using the method of moments (MoM). The analysis is performed with 2L y
TL;DR: In this article, a material combining both mirror-conjugated and racemic chirality properties is characterized and classified within the context of linear bianisotropic mediums, with particular emphasis on the interaction of different and no handedness along certain specified directions.
Abstract: A material combining both mirror-conjugated and racemic chirality properties is characterized and classified within the context of linear bianisotropic mediums. Planewave propagation in the chosen material is studied with particular emphasis on the interaction of different and no handedness along certain specified directions. Comparison is made with isotropic chiral mediums as well as uniaxial bianisotropic mediums.
TL;DR: In this paper, the backscattering enhancement can be predicted from the constructive interference of multiple surfaces scattering from a very roughly random surface, and it is shown that for specialized surfaces involving roughness large compared with the incident wavelength, the back scattering enhancement takes place.
Abstract: Predictions for scattering from randomly very rough surfaces are developed and compared with experimental data. The integral equation method with multiple scattering is developed to predict this backscattering enhancement phenomenon. The backscattering enhancement can be predicted from the constructive interference of multiple surfaces scattering from a very roughly random surface. For specialized surfaces involving roughness large compared with the incident wavelength, the backscattering enhancement takes place. In this paper we show that the phenomenon of backscattering enhancement becomes evident for both the normalized surface height > 1.5 and the surface root mean square slope > 0.5. Further, we also show that the incident angle is a factor for the backscattering enhancement. The derivation of the basic surface scattering model is provided and a computer simulation is also provided to compare with measurement. The phenomenon of backscattering enhancement is observed in both the integral equatio...
TL;DR: In this paper, the electromagnetic continuity condition is extended from the classical condition on an interface between two media to a more general one relating sources and fields in a region between two regions of arbitrary media.
Abstract: The electromagnetic continuity condition is extended from the classical condition on an interface between two media to a more general one relating sources and fields in a region between two regions of arbitrary media. The condition allows one to extend the classical Huygens principle to involve equivalent sources in a spatial region volume or on multiple surfaces. As an example, the generalized Huygens principle is applied to the formulation of a scattering problem in terms of a surface integral equation. Also, the transparent absorbing boundary (TAB) condition can be interpreted in terms of the extended Huygens principle.
TL;DR: In this article, two numerical strategies are developed to model the electromagnetic propagation across different dielectric media. And the numerical accuracy of the proposed technique has been validated by comparison with theoretical results.
Abstract: The characteristic-basedfinite-volume time-domain method is applied to analyze the scattering from conducting objects coated with lossy dielectric materials. Based on the characteristic-based finite-volume scheme, two numerical strategies are developed to model the electromagnetic propagation across different dielectricmedia. One introduces a connecting boundary to separate the total-field region from the scattered-field region. The other employs the scattered field formulation throughout the computational domain. These two strategies are verified by numerical experiments to be basically equivalent. A numerical procedure compatible with the finite-volume scheme is developed to guarantee the continuity of the tangential electric and magnetic fields at the dielectric interface. Rigorous boundary conditions for all the field components are formulated on the surface of the perfect electric conducting ( ) PEC objects. The numerical accuracy of the proposed technique has been validated by comparison with theoretical results.
TL;DR: In this article, a two-arm spiral antenna printed on a finite-sized dielectric substrate backed by an infinite-sized conducting plane is analyzed using the finite-difference time-domain method (FDTDM).
Abstract: A two-arm spiral antenna printed on a finite-sized dielectric substrate backed by an infinite-sized conducting plane is analyzed using the finite-difference time-domain method (FDTDM). The antenna is fed by a vertical probe located at the center of the antenna. The antenna height above the ground plane is 0.147 wavelength. The FDTDM analysis reveals that the antenna forms an elliptically polarized conical beam. Based on this investigation, two parasitic elements are introduced near the vertical feed probe to obtain a circularly polarized conical beam. It is found that the current on the vertical feed probe is approximately 180 out of phase with the currents on the two parasitic elements. This results in a reduction in the radiation from the feed probe, with a corresponding improvement in the axial ratio. The frequency response of the antenna with the parasitic elements is also calculated. The angle of maximum radiation is approximately θmax 54 for a bandwidth of m 6.2% (0.982f to 1.044f). Within this freq...
TL;DR: In this article, it was shown that a TEM plane wave with inhomogeneous constitutive parameters can be used for generating dispersionless bends in high-voltage transmission systems in which the pulse rise time is small compared to transit times across the transmission line (e.g., coax) cross section.
Abstract: A recent result showed that guided transverse electromagnetic (TEM) waves of a very general form could be propagated in an inhomogeneous isotropic dielectric medium with permittivity proportional to Psi-2, where Psi is the cylindrical radius in the usual (Psi,phi,z) cylindrical coordinate system. This has the important property that the permeability mu can be taken as mu0, a constant. Moreover, very general conductor cross sections in (z ,Psi)coordinates can be specified. This allows for the construction of dispersionless bends in high-voltage transmission systems in which the pulse rise time is small compared to transit times across the transmission-line (e.g., coax) cross section. This is important for high-power pulse sources and antennas. The analysis shows that while the permeability can be allowed to be variable, the choice of mu=mu0 allows one to specify purely dielectric lenses. Thus the generalized form of a TEM plane wave involving inhomogeneous constitutive parameters can be used for generating...
TL;DR: In this paper, a three-dimensional analysis of magnetic field and axial coupling of multipole disk magnets is presented based on the Fourier transform, the field, torque, and force can be obtained by a pair of Fourier transforms, a spatial filtering, and summations.
Abstract: A three-dimensional analysis of magnetic field and axial coupling of multipole disk magnets is presented. Based on the Fourier transform, the field, torque, and force can be obtained by a pair of Fourier transforms, a spatial filtering, and summations. The computed results agree well with the results given by the finite element method or experiments.
TL;DR: In this article, a physical-optics solution to the three-dimensional problem of dipole radiation over an arbitrary-angled wedge is presented, where the medium beneath each face of the wedge is nonmagnetic, lossy, and not necessarily the same for both faces.
Abstract: A physical-optics (PO) solution to the three-dimensional problem of dipole radiation over an arbitrary-angled wedge is presented. The medium beneath each face of the wedge is nonmagnetic, lossy, and not necessarily the same for both faces. Excitation is provided by an electric dipole that is parallel to the edge of the wedge. The analytical formulation is based on the Stratton-Chu formula. The electromagnetic (EM) field due to a horizontal electric dipole over a lossy half-space is used on the faces and a charge distribution along the edge is introduced to account for the discontinuity of the EM field across the edge. The integral expression for the electric-field intensity far from the edge is evaluated asymptotically, thus resulting in a formula that is uniformly valid. The validity of this edge-corrected PO solution is established through a reciprocity check and comparisons with other solutions.
TL;DR: In this article, a modified integral equation model for the bistatic surface scattering from a randomly rough surface is developed based upon an approximation of a pair of integral equations and a shadowing function for the tangential surface fields.
Abstract: This paper addresses the bistatic multiple surface scattering from perfectly conducting rough surfaces. A modified integral equation model for the bistatic surface scattering from a randomly rough surface is developed based upon an approximation of a pair of integral equations and a shadowing function for the tangential surface fields. Existing integral equation models without a shadowing function and the separation of upward and downward scattering cannot estimate correctly the scattering behavior of bistatic multiple surface scattering. In this paper the tangential surface fields, average scattered power, and bistatic-like and cross-polarized reflectivities from a randomly rough surface are formulated with the shadowing function. The effect of multiple surface scattering in the bistatic direction is analyzed. Further comparisons of this modified integral equation model with measurements show agreements to within a dB in bistatic scattering.
TL;DR: In this paper, an array composed of spiral elements, each having a small number of turns, is numerically analyzed and a technique of using parasitic wires around the feed wire is presented.
Abstract: An array composed of spiral elements, each having a small number of turns, is numerically analyzed. The spiral elements are circularly arrayed above a ground plane and are excited by a single vertical feed wire. As the number of the spiral elements increases, the copolarization component of the radiation becomes omnidirectional. The maximum variation in the copolarization component as a function of azimuth angle is 0.8 dB for four spiral elements. Attention is also paid to an improvement in the axial ratio. A technique of using parasitic wires around the feed wire is presented. Calculations show that, when the distance between the feed wire for four spiral elements and the parasitic wires is appropriately chosen, the axial ratio is improved. The 3-dB axial ratio frequency bandwidth evaluated in the maximum beam direction is found to be 10%. Within this bandwidth, the gain is more than 5 dB.
TL;DR: In this paper, the dispersion dyadics of the materials seen by the eigenwaves are derived and the refractive indices are solved for arbitrary direction of propagation for plane-wave propagation in the most general bianisotropic medium.
Abstract: Plane-wave propagation is studied in the most general bianisotropic medium in which the electromagnetic wave can be split into two eigenwaves with certain polarizations depending on two arbitrary directions in space. Hence the whole problem splits into two parts. The dispersion dyadics of the materials seen by the eigenwaves are derived and the refractive indices are solved for arbitrary direction of propagation. Also, a general expression for the eigenpolarizations is found. The theory is applied to some cases fitting the requirements of the media.
TL;DR: In this paper, a special issue on Spiral Antennas is presented, with a focus on the Spiral Antenna and its applications in magnetics and electromagnetics, where the authors discuss the following topics:
Abstract: (2000). Guest Editor's Comments: Special Issue on Spiral Antennas. Electromagnetics: Vol. 20, No. 4, pp. 269-270.
TL;DR: In this paper, a plane wave diffraction by two impedance halfplanes joined together by a resistive step is studied using the Fourier transform technique, which is formulated as a pair of uncoupled modified Wiener-Hopf equations and solved approximately.
Abstract: Plane wave diffraction by two impedance half-planes joined together by a resistive step is studied. By using the Fourier transform technique, the problem is formulated as a pair of uncoupled modified Wiener-Hopf equations and solved approximately.Numerical results illustrating the effects of various parameters such as step height, step resistivity, plate impedances, etc., on the diffraction phenomenon are presented.
TL;DR: Analytic Fourier series admit a uniform exponential truncation bound and this leads to pertinent truncation bounds for the multipole potential expansion in the fast multipole method.
Abstract: Analytic Fourier series admit a uniform exponential truncation bound. Applied to the fast multipole method this leads to pertinent truncation bounds for the multipole potential expansion.
TL;DR: In this paper, an asimplified integral equation for a dielectric-coated antenna composed of arbitrarily connected straight-wire segments is formulated in a Hallen-type form.
Abstract: Asimplified integral equation for a dielectric-coated antenna composed of arbitrarily connected straight-wire segments is formulated in a Hallen-type form. The derived integral equation contains only a single integral for numerical procedures. The current distribution obtained for a short helical antenna coated with dielectric material agrees with that for previously published results. As an application of the integral equation, a rectangular spiral antenna is analyzed to show the effects of dielectric coating on the radiation fields.
TL;DR: In this article, a rigorous mode-matching technique is implemented for the study of the unloaded Q factor of a dielectric resonator operating in the TE01delta, TM01-delta, and HEM11delta modes.
Abstract: A rigorous mode-matching technique is implemented for the study of the unloaded Q factor of a dielectric resonator operating in the TE01delta , TM01delta , and HEM11delta modes. The cylindrical dielectric resonator is loaded into a metal enclosure and placed on a dielectric substrate. The analysis permits the calculation of the loss introduced by the resonator parameters and also the electromagnetic energy distribution inside the cavity. Numerical results are presented demonstrating the variation of the unloaded Q factor, electromagnetic energy distribution, and power loss against geometrical and material parameters. Finally, the accuracy of the calculations is verified with comparison with another rigorous method.
TL;DR: In this paper, an extrapolated version of Gordon's interpolation is applied to a generalized version of the volume surface integral equation to solve two-dimensional scattering problems, which results in the decomposition of the problem into three simpler independent problems which can be performed either in sequence or in parallel.
Abstract: When applied to the electromagnetic scattering problem, the method of moments (MoM) results in a full matrix representation which requires a large amount of computational resources. To circumvent this problem, the numerical technique presented here works directly on the efficiency of the interpolation scheme used in the MoM, introducing an extrapolated version of Gordon's interpolation. This new method is applied to a generalized version of the volume surface integral equation to solve two-dimensional scattering problems. It is shown how it results in the decomposition of the problem into three simpler independent problems which can be performed either in sequence or in parallel. The performances of the method are confirmed by convergence tests, and the extrapolated MoM is illustrated on the case of the scattering by a microstrip structure.