Showing papers in "Electromagnetics in 1986"
TL;DR: The occurrence of exponentially increasing instabilities is a common feature of time marching methods for solving transient scattering problems as discussed by the authors, and the mechanism by which such instabilities arise and various methods of reducing their effect are described.
Abstract: The occurrence of exponentially increasing instabilities is a common feature of time marching methods for. solving transient scattering problems. In this paper we consider the mechanism by which such instabilities arise and describe various methods of reducing their effect.
64 citations
TL;DR: In this paper, the complete eigenfunction expansion of the electric field dyadic Green's function in spherical coordinates is presented with particular attention given to the significance of the longitudinal eigenfunctions in this expansion.
Abstract: The complete eigenfunction expansion of the electric field dyadic Green's function in spherical coordinates is presented with particular attention given to the significance of the longitudinal eigenfunctions in this expansion. It is shown that the spectrum of the transverse eigenfunctions contribute zero frequency static like modes that cancel the longitudinal modes outside the source region. Inside the source region the cancellation is not complete but the non-cancelling part can be expressed as a delta function contribution in full agreement with the results obtained by Tai by a different method. Various representations for the dyadic Green's function in free space and in a spherical cavity are presented. The paper includes a brief historical survey of the development of the eigenfunction expansion method for the dyadic Green's function in order to highlight some of the early difficulties that were encountered.
36 citations
TL;DR: In this paper, a recurrence/continued fraction algorithm was proposed for the evaluation of the Green's function pertinent to this particular configuration of printed circuit elements. But this algorithm is not suitable for the case of large cylinders.
Abstract: This article presents the solution to the heretofore unresolved problem of precise computation for the near field of printed circuits and printed circuit antennas on cylindrical substrates. The procedure involves a recurrence/continued fraction algorithm development for the evaluation of the Green's function pertinent to this particular configuration of printed circuit elements. With this new algorithm, arbitrary size cylindrical substrates can be modelled with an extremely high degree of accuracy. Computation of the input impedance of center fed and axially symmetric microstrip dipoles is used as an example. Excellent agreement is found for large cylinders with the limiting case of center fed microstrip dipoles on planar substrates.
36 citations
18 citations
TL;DR: The application of MULTICONDUCTOR TRANSMISSION LINE NETWORK ANALYSIS to INTERNAL INTERACTION PROBLEMS is discussed in this paper, where the authors present a framework for the analysis of multichannel communication networks.
Abstract: (1986). APPLICATION OF MULTICONDUCTOR TRANSMISSION LINE NETWORK ANALYSIS TO INTERNAL INTERACTION PROBLEMS. Electromagnetics: Vol. 6, No. 1, pp. 1-20.
17 citations
TL;DR: In this article, an analytical technique used is the generalized transmission line method, which has the advantage of estimating the phase of aperture fields correctly, and the theoretical and measured characteristics of annular sector antenna are found to be good Semicircular annular ring antenna appears to be promising
Abstract: Annular sector and circular sector microstrip antennas have been analyzed for input impedance and radiation patterns The analytical technique used is the generalized transmission line method which has the advantage of estimating the phase of aperture fields correctly Agreement between the theoretical and the measured characteristics of annular sector antenna are found to be good Semicircular annular ring antenna appears to be promising
13 citations
TL;DR: In this article, a decomposition of the pertinent Green's function, using weighted image theory, into two smooth-valued perturbation terms and a singularity containing term is presented.
Abstract: This article presents a method which models printed circuit antennas with very high efficiency. The model is based on a decomposition of the pertinent Green's function, using weighted image theory, into two smooth-valued perturbation terms and a singularity containing term which can be treated analytically. This, in addition to the adoptation of a numerical interpolation technique, leads to minimization of computation time when the method of moments is enforced. An analytic-numeric real axis integration approach is also applied to evaluate the near field quantity of the perturbation terms.
11 citations
TL;DR: In this article, it is shown that the discrete system associated with the Spectral Iterative Technique (SIT) is equivalent to a moment method matrix equation, with basis and testing functions chosen implicitly in the process.
Abstract: : It is shown that the discrete system solved by the Spectral Iterative Technique (SIT) is of Toeplitz or block Toeplitz form, and thus may be more amenable to direct solution in certain cases. In addition, the discrete system associated with the SIT is shown to be equivalent to a moment method matrix equation, with basis and testing functions chosen implicitly in the process. Thus, there is no additional generality in the SIT type of approach compared to the conventional method of moments. These statements concern the discretization procedure used within the SIT, and apply whether the SIT is implemented in its original form or in connection with the conjugate gradient method. Simple examples of scattering from a single strip and from a periodic array of strips are used to illustrate the concepts. (JHD)
9 citations
TL;DR: The architecture for an expert system for use in the EMP hardening of complicated systems, such as aircraft and ships is developed, and a specific graph model is explored as a candidate data base structure, and examples of the use of this data base are shown.
Abstract: This paper develops the architecture for an expert system for use in the EMP hardening of complicated systems, such as aircraft and ships. The best form for the topology knowledge base is one that mimics the topology data base: graphic. A specific graph model is explored as a candidate data base structure, and examples of the use of this data base are shown.
7 citations
TL;DR: In this paper, a renormalizing procedure for the N-wave variables and scattering matrix based on a real-power condition is defined for use with electromagnetic topology, a most significant result concerns the minimization of the norm of the scattering matrix leading to a choice of a real conductance matrix times the identity matrix as the normalizing admittance matrix.
Abstract: Scattering matrices play an important role in transmission-line network, theory and in electromagnetic topology. Norms of such matrices are used in bounding system response. Using power considerations, bounds for the 2-norm of such matrices can be found. Appropriate constraints on the normalizing admittance (impedance) matrix for the N waves defining the scattering matrix are made. A renormalizing procedure is defined for the N-wave variables and scattering matrix based on a real-power condition. For use with electromagnetic topology, a most significant result concerns the minimization of the norm of the scattering matrix leading to a choice of a real conductance matrix times the identity matrix as the normalizing admittance matrix.
6 citations
TL;DR: In this article, both the line and aperture penetrations are included in the scattering matrix formulation and experimental and analytical methods are proposed for the determination of the elements of the scattering matrices corresponding to these penetrations.
Abstract: Scattering matrices of subshields and their norms have been used to relate the internal signals of an enclosed volume to an electromagnetic source environment. Both the line and aperture penetrations are included in the scattering matrix formulation. Experimental and analytical methods are proposed for the determination of the elements of the scattering matrices corresponding to these penetrations. These methods can, in turn, be used to analyze the overall shielding performance and to allocate the subshield electromagnetic hardening requirements of a system. Limitations and assumptions in using this electromagnetic topology technique are also addressed.
TL;DR: A recently developed antenna pattern reconstruction technique using the nonuniform sampling algorithm is able to construct the antenna far-field patterns from a set of non-uniformly distributed amplitude and phase samples.
Abstract: A recently developed antenna pattern reconstruction technique using the nonuniform sampling algorithm is able to construct the antenna far-field patterns from a set of non-uniformly distributed amplitude and phase samples. This paper presents the application of this technique to an actual antenna measurement performed at JPL. The 1.47-meter Viking and a 1-meter reflectors operating at X-band were both measured. A conical-cut approach is used to generate nonuniformly distributed samples. The far-field patterns of these two antennas are reconstructed from the measured data using a developed computer program based on the nonuniform sampling algorithm. An overlapping “Window Concept” is also applied in the far-field reconstruction process to avoid measurement error spreading. The results of the reconstructed patterns are compared with the standard azimuth-cut patterns. The effects of selection of various phase reference points in applying the nonuniform sampling technique are demonstrated through a n...
TL;DR: In this article, the authors present a simple theory which establishes the plausibility of this upper bound in the case of a leader tip and compare the results of the basic theory to more complex treatments applied to nuclear lightning.
Abstract: Frequently in the lightning literature the upper bound on the rate of rise of lightning current of the order of 1011 A/s or a few times this appears. There is currently no theoretical explanation for this limit or the probability distribution around this maximum. In this paper we present a simple theory which establishes the plausibility of this limit in the case of a leader tip. We also compare the results of the basic theory to more complex treatments applied to nuclear lightning.
TL;DR: In this article, the surface divergence of the surface current density on a perfectly conducting object is measured, which is related to the surface charge density, or the normal electric field, and a complementary quantity, the surface curl of thesurface current density, which can be related to an equivalent magnetic charge density and the normal derivative of the normal magnetic field.
Abstract: It is commonplace to measure the surface divergence of the surface current density on a perfectly conducting object. This is related to the surface charge density, or the normal electric field. This paper explores the measurement or a complementary quantity, the surface curl of the surface current density which can be related to an equivalent magnetic charge density, or the normal derivative of the normal magnetic field. Techniques and difficulties are discussed.
TL;DR: In this article, a new method is proposed for the evaluation of the capacity of flat laminae of arbitrary shape based on an integral representation for the reciprocal distance between two points obtained by the author earlier.
Abstract: A new method is proposed for the evaluation of the capacity of flat laminae of arbitrary shape. The method is based on an integral representation for the reciprocal distance between two points obtained by the author earlier. Specific approximate formulae are derived for evaluating the capacity of a polygon, a triangle, a rectangle, a rhombus, a circular rector and a circular segment. All the formulae are checked against the solutions known in the literature, and a good accuracy is confirmed. No similar formulae have ever been reported.
TL;DR: In this paper, the mutual coupling of the array elements was determined using the reaction theorem, which provided both array patterns and the active impedance of the elements, and was then used to study a 19-element array for MSAT application.
Abstract: The radiation characteristics of small microstrip arrays is investigated including the mutual coupling effects among the array elements. The mutual coupling of the elements is determined using the reaction theorem, which provides both array patterns and the active Impedances of the elements. The method is then used to study a 19-element array for MSAT application. For the array elements circular patch microstrip antennas are used and optimized to give satisfactory circularly polarized radiation. For the 19-element array, it is shown that the array gain decreases by scanning the array beam towards the endfire direction and a peak gain of 13.73 dBi. is obtained at an elevation angle of 57 degrees. Further scanning of the beam, towards lower elevation angles, reduces the array gain further.
TL;DR: Practical reduction in the number of analytical operations required to partition large systems into tractable pieces is described, by invoking the principle of effectively impervious shields.
Abstract: The use of shield topology Co partition large systems into tractable pieces is discussed. The interactions of externally generated transients with large systems are discussed from the aspect of the numbers of operations that must be considered. The segments of interaction associated with multiple shield imperfections, multiple levels of shields, system states, and abnormal modes lead to enormous numbers of analytical operations that must be performed to evaluate a family of responses. Practical reduction in this number, by invoking the principle of effectively impervious shields, is described.
TL;DR: In this article, the radiation characteristics of radial rib reflector antennas are studied using both an exact physical optics analysis and a simplified approximate analysis in order to understand the behavior of the rib-related sidelobes which have a cyclic behavior in the azimuthal direction.
Abstract: The radiation characteristics of radial rib reflector antennas are studied. This type of antenna can be used as a large deployable satellite antenna. The radiation patterns of a axi-symmetric reflector are computed using both an exact physical optics analysis and a simplified approximate analysis in order to understand the behaviour of the rib-related sidelobes which have a cyclic behaviour in the azimuthal direction. A parametric study is conducted. A shaped sub-reflector is designed using diffraction profile synthesis to compensate for some of the errors introduced by the main radial rib reflector.
TL;DR: This report contains criteria to guide the design of labelling schemes, some specific schemes are presented and illustrated for a sample topology, and satisfaction of the criteria is discussed.
Abstract: : This report defines the problems associated with applying graph theory to interaction sequence diagrams used in electromagnetic topology. Because few applications have been developed, the optimal labelling scheme has yet to emerge. As a result, operations on the graph are difficult to record concisely. This report contains criteria to guide the design of labelling schemes. Some specific schemes are presented and illustrated for a sample topology, and satisfaction of the criteria is discussed. (Author)
TL;DR: The boundary conditions necessary to support hybrid modes in round waveguide are derived in this article, where the transverse field over the open mouth of the guide is found and the Fourier transform of this field is then used to calculate far field radiation patterns.
Abstract: Hybrid mode horns are of considerable practical importance, especially as feeds for lens and reflector antennas. In this tutorial review the boundary conditions necessary to support hybrid modes in round waveguide are derived. Expressions for the field components in HE1n and EH1n modes are given and from these the transverse field over the open mouth of the guide is found. The Fourier transform of this field is then used to calculate far field radiation patterns. Solutions to the characteristic equation for hybrid modes are indicated and the dispersion characteristics for balanced modes are presented graphically. Finally, a brief discussion of dielectric-lined waveguide is given and asymptotic solutions are developed to show that nearly balanced HE11 and EH11 modes can exist over a limited frequency range when the dielectric is lossless, but over an unlimited range when the dielectric is highly lossy.
TL;DR: In this paper, a cylindrical dielectric rod is interpreted in terms of the resonances at which these helical surface waves azimuthally match phases after each circumnavigation of the rod, effectively forming resonating standing waves around the rod.
Abstract: The conventional formulation of the electromagnetic field solution for a cylindrical dielectric rod is re-interpreted in a novel fashion in order to show the presence of surface waves which propagate over the rod's surface along helical paths. The solutions of the characteristic equation of the rod are interpreted in terms of the resonances at which these helical surface waves azimuthally match phases after each circumnavigation of the rod, effectively forming resonating standing waves around the rod. This interpretation permits us to obtain the pitch angle of the helix, and the dispersion curves (phase velocity as a function of frequency) of the helical surface waves.
TL;DR: In this article, the phase characteristics of the antenna as a function of the observation angle were investigated with several groundplane types using slot theory and the Uniform Theory of Diffraction (UTD) for their application in GPS.
Abstract: In the use of satellite positioning systems such as the Global Positioning System (GPS) significant errors can be introduced into the indicated position through the properties of the antenna structure. Of particular interest are the phase characteristics of the antenna as a function of observation angle. The microstrip antenna features a rugged, low profile and light weight construction making it an ideal choice for practical applications, but positioning accuracy may be limited by the phase perturbations introduced by the microstrip mounting surface. The rectangular microstrip and narrow slot antennas are investigated with several groundplane types using slot theory and the Uniform Theory of Diffraction (UTD) for their applicability in GPS. Amplitude, phase and phase centre characteristics are studied with particular emphasis on the pattern response at low elevation angles which are of particular interest in hydrographic and aviation applications. Analytic and experimental data are presented to ...
TL;DR: In this paper, the effect of the offset angle on the peak cross-polarization level of the dual parabolic cylindrical reflectors was analyzed and a design procedure for such an offset configuration was provided.
Abstract: The offset dual parabolic cylindrical reflectors are analyzed. They generally produce elliptical beam patterns with unequal beamwidths in the two principal planes. The dependence of the principal plane beamwidths, the peak cross-polarization level, the antenna gain and the first sidelobe level on the antenna geometrical parameters, and in particular the offset angle, is studied. The main effect of the offset angle is increasing the cross-polarization level. However, for any offset configuration, the angle between the two reflectors has a strong effect on the cross-polarization. Optimizing this angle, the peak cross-polarization may become negligibly small, and as low as -60dB. A design procedure for such an offset configuration is provided and a design example Is given.