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Antennas and Propagation, IEEE Transactions on

Issue 8 • Date Aug. 1994

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Displaying Results 1 - 24 of 24
  • Comments on "Scattering from conducting rough surfaces: a general perturbative solution" [with reply]

    Page(s): 1198 - 1199
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    The author comments that Vazouras et al. (see ibid. vol.41, no.9, p.1232-1241, 1993) presented an analysis leading to the general term of the perturbation series for scattering of horizontally polarized plane incident waves from a perfectly conducting rough surface. Other than Rice's 1951 seminal paper, they mention none of the other early work on this topic. Beyond this lack of references to other than the most recent work, however, Vazouras et al. state, "thus it seems that the scope of perturbation methods is considerably restricted by the fact that the general term of the perturbation series was, until recently, unknown." I (see RadioSci., vol.12, no. 5, p.719-729, 1977) was the first to derive the general term of a perturbation series for electromagnetic scattering from a rough surface. Vazouras et al. reply that the criterion for the selection of previous work cited in our paper was one of topic relevance rather than of chronological order. In view of the large amount of literature pertinent to the region of interest, we chose to mention mainly works dealing with the foundation of the particular class of perturbation solutions developed within the framework of the extended boundary condition, thus being important to the course of our treatment, plus some works the results of which we were explicitly commenting.<> View full abstract»

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  • Comments on "An exact formulation for the vector potential of a cylindrical antenna with uniformly distributed current and arbitrary radius" [with reply]

    Page(s): 1200 - 1202
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    The paper written by Werner (see ibid, vol.41, no.8, p.1009-1018, 1993) relies on the technique and results that were developed by Overfelt (1987). At the time, I submitted a comment regarding that method (see. Gera, ibid. p.584, 1990). It seems that this comment applies here. Werner replies that the exact expressions for the generalised exponential integral are mathematically correct in the form that they appear in the paper, as demonstrated by the results shown. There are actually several equivalent forms which exist for these expansions.<> View full abstract»

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  • Multiple cluster beamspace and resolution-enhanced ESPRIT

    Page(s): 1041 - 1052
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    This paper addresses approaches to enhancement of the resolution of one or more clusters of closely spaced emitters. The TLS-ESPRIT algorithm is considered, as applied in beamspace and in element space, in conjunction with resolution enhancement. Beamspace (BS)-ESPRIT employs a matrix beamformer as a preprocessor to map the sensor space into a lower dimensional beamspace. Resolution enhanced (RE)ESPRIT employs a matrix beamformer as a left weighting of the signal subspace eigenvector matrix for enhancing the resolution of ESPRIT. This paper specifically discusses several types of these beamformer matrices, which differ in the way that they treat source clusters other than of interest. Our objective is to clearly define approaches and identify their relative merits, through discussion and illustrative simulation, so as to provide an understanding of how to proceed in designing an ESPRIT algorithm View full abstract»

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  • Surface-ray tracing on hybrid surfaces of revolution for UTD mutual coupling analysis

    Page(s): 1167 - 1175
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    An angle invariance property based on Hertz's principle of particle dynamics is employed to facilitate the surface-ray tracing on nondevelopable hybrid quadric surfaces of revolution (h-QUASOR's). This property, when used in conjunction with a geodesic constant method, yields analytical expressions for all the ray-parameters required in the UTD formulation. Differential geometrical considerations require that some of the ray-parameters (defined heuristically in the UTD for the canonical convex surfaces) be modified before the UTD can be applied to such hybrid surfaces. Mutual coupling results for finite-dimensional slots have been presented as an example on a satellite launch vehicle modeled by general paraboloid of revolution and right circular cylinder View full abstract»

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  • A theoretical and numerical analysis of the measured equation of invariance

    Page(s): 1097 - 1105
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    The measured equation of invariance (MEI) has been previously introduced to efficiently and accurately handle the boundary truncation for finite methods. The present authors give a theoretical analysis that provides several important insights into the capabilities of the MEI. From the numerical study, they can explain why the MEI works better than one would expect. Both the theoretical and the numerical analyses demonstrate that the accuracy of the solution is dependent on the electrical size of the geometry as well as the distance between the mesh boundary and the geometry. From the analysis, the authors propose a new set of metrons that is less sensitive to the excitation than the previously proposed sinusoidal metrons View full abstract»

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  • Polarimetric scattering from a layer of random clusters of small spheroids

    Page(s): 1138 - 1144
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    Employing the volume integral equation formulation with self-interaction term for internal fields, the Jones scattering matrix and phase matrix for random clusters of small spheroids are derived. The mutual coherent wave interactions among clustered spheroids are included. Clustering enhances the internal fields and the scattering amplitude function. Substituting the newly derived phase matrix into the Mueller matrix in the approach of vector radiative transfer for a layer of random clusters of small spheroids, fully polarimetric copolarized and cross-polarized backscattering are numerically calculated. Clustering effects of a layer of random spheroids are quantitatively illustrated, and the backscattering enhancement of several dB order and its functional dependence on parameters are discussed View full abstract»

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  • A self-steered array system for microwave communications

    Page(s): 1192 - 1195
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    The paper presents a self-steered algorithm that can be used to correct pointing errors in microwave communications. The algorithm is based on the fact that the output power of an optimized beamformer achieves a local maximum if the steering vector coincides with that of the desired signal, as long as the interferences are outside the mainbeam. By approximating the steering vector by its first-order Taylor series expansion in terms of the steering angles, the maximization process reduces to a two-dimensional optimization problem. Numerical results are presented to illustrate the performance achievable View full abstract»

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  • Simple and accurate formula for the resonant frequency of the equilateral triangular microstrip patch antenna

    Page(s): 1178 - 1179
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    An approximate solution of the capacitance of a circular microstrip disk to account for the fringing fields is used for calculation of the resonant frequency formula of the equilateral triangular microstrip patch antenna. The theoretical results are in good agreement with experimental data View full abstract»

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  • The active element pattern

    Page(s): 1176 - 1178
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    This review article discusses the use of the active element pattern for prediction of the scan performance of large phased array antennas. The introduction and application of the concept of the active element pattern goes back at least 30 years but the subject is generally not covered in modern antenna engineering textbooks or handbooks, and many contemporary workers are unfamiliar with this simple but powerful idea. In addition, early references on this subject do not provide a rigorous discussion or derivation of the active element pattern, relying instead on a more qualitative interpretation. The purpose of this article is to make the technique of active element patterns more accessible to antenna engineers, and to provide a new derivation of the basic active element pattern relations in terms of scattering parameters View full abstract»

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  • Retarded time absorbing boundary conditions

    Page(s): 1059 - 1064
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    Over the past few years simulations of electromagnetic problems in three dimensions using the finite difference time domain (FDTD) method have become increasingly popular. A major problem in such simulations is the truncation of the computational domain. A formulation of this boundary problem using retarded time values of the field inside the computational domain is suggested, and hence the name retarded time absorbing boundary condition (RT-ABC). This formulation allows the boundary to be situated in the near field of the problem and thereby reduces the necessary computational domain, and the present formulation allows error estimates for the numerically calculated fields View full abstract»

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  • Waveguide excited microstrip patch antenna-theory and experiment

    Page(s): 1114 - 1125
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    An arbitrarily shaped microstrip patch antenna excited through an arbitrarily shaped aperture in the mouth of a rectangular waveguide is investigated theoretically and experimentally. The metallic patch resides on a dielectric substrate grounded by the waveguide flange and may be covered by a dielectric superstrate. The substrate (and superstrate, if present) consists of one or more planar, homogeneous layers, which may exhibit uniaxial anisotropy. The analysis is based on the space domain integral equation approach. More specifically, the Green's functions for the layered medium and the waveguide are used to formulate a coupled set of integral equations for the patch current and the aperture electric field. The layered medium Green's function is expressed in terms of Sommerfeld-type integrals and the waveguide Green's function in terms of Floquet series, which are both accelerated to reduce the computational effort. The coupled integral equations are solved by the method of moments using vector basis functions defined over triangular subdomains. The dominant mode reflection coefficient in the waveguide and the far-field radiation patterns are then found from the computed aperture field and patch current distributions. The radar cross section (RCS) of a plane-wave excited structure is obtained in a like manner. Sample numerical results are presented and are found to be in good agreement with measurements and with published data View full abstract»

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  • Modeling baluns with the method of moments

    Page(s): 1195 - 1198
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    When using the method of moments (MoM) to model large arrays with large numbers of balanced feeds, the feed baluns can always be incorporated into the analysis by combining the multiport admittance matrix for the array with the admittance matrices of the baluns. This technique is straightforward but requires that the MoM equations be solved for a large number of right-hand sides. The paper shows how the effects of perfect baluns can be incorporated directly into the MoM equations, requiring only one right-hand side. This technique yields the exact results with a significant savings in computing resources View full abstract»

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  • Scattering from a conductive rectangular plate covered by a thick dielectric layer and excited from a dipole source or a plane wave

    Page(s): 1065 - 1076
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    The scattering of electromagnetic radiation from a conductive rectangular plate of infinitesimal thickness covered by a dielectric parallelepiped of arbitrary size is analyzed. An integral equation formulation is employed in terms of the electric field inside the dielectric layer and the surface current density on the conductive plate, and is solved approximately by using entire domain Galerkin technique. The electric field inside the dielectric layer is described in terms of a superposition of exponential waves while, in describing the surface current density on the conductive plate, two types of entire domain basis functions are utilized: either Fourier-exponential series or Chebyshev series type finite-term expansions are employed alternatively. Numerical results are computed and presented for several scatterer sizes and excitation types View full abstract»

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  • The phase center position of a microstrip horn radiating in an infinite parallel-plate waveguide

    Page(s): 1185 - 1188
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    In this paper the field radiated by a flared microstrip line in an infinite parallel-plate waveguide with separation between plates of less than half a wavelength is studied. The field at any point of the parallel-plate waveguide is expressed as a summation of modal solutions of the Helmholtz equation. The phase center of the microstrip horn is calculated for uniform amplitude distributions along the horn aperture. The theory may be applied to obtain the phase and amplitude distributions along the output ports of microstrip bootlace lenses View full abstract»

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  • A design procedure for classical offset dual reflector antennas with circular apertures

    Page(s): 1145 - 1153
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    A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors View full abstract»

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  • Moment method analysis of infinite stripline-fed tapered slot antenna arrays with a ground plane

    Page(s): 1161 - 1166
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    A full-wave method of moments solution for infinite arrays of stripline-fed tapered slot antennas is described. The formulation of the problem is sufficiently general to permit performance evaluation of most of the geometries that have been proposed for stripline-fed antennas as well as of several other types of array antennas. Computed results for some well-known antenna arrays are presented to demonstrate the validity and accuracy of the method. Excellent agreement with published results has been obtained for scattering from corrugated surfaces and grounded dielectric slabs and for the input impedance of dipole and monopole arrays. Catastrophic effects such as scan blindness are accurately predicted. A sample result showing the measured and computed input impedance of a stripline-fed tapered slot antenna array is also presented View full abstract»

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  • Prediction models and measurements of microwave signals scattered from buildings

    Page(s): 1126 - 1137
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    The planning of urban microwave communication systems must consider the harmful interference these systems cause to existing links, and vice versa. Site shielding is an interference reduction technique wherein a building is used deliberately to shield a radio terminal from interfering signal. The site-shielding factor (SSF) is, however, influenced by the arrival of interference on paths caused by reflection and scatter from nearby buildings. Prediction models are needed to estimate the effects arising from the scatter. The paper develops prediction models based on a plane reflector and discusses experimental measurements aimed at the validation of these models. The paper describes the results of the initial stage of a continuing investigation into building scatter aimed at the formulation of a prediction procedure for site shielding suitable for radio system planning and coordination View full abstract»

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  • Analysis of a dual circularly polarized microstrip antenna fed by crossed slots

    Page(s): 1053 - 1058
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    A dual circularly polarized, wideband microstrip antenna fed by two perpendicular crossed slots is analyzed in this work. The cross shaped aperture in the ground plane provides coupling between the microstrip patch and a single microstrip line underneath the ground plane, traversing the four arms of the cross in a serial manner, thereby generating four coupling points in phase quadratures for both senses of circular polarization. The analysis of this antenna incorporates two stages: In the first one, the individual load impedances are computed via an integral equation based on reciprocity, assuming no interactions between the ports. The second stage employs a transmission line model where the four coupling points are considered as lumped loads along the feed line. An iterative scheme employs the transmission line model for the determination of the actual impedances of each coupling point, including the mutual interactions with the other coupling points. This procedure provides control over the overall level of radiated energy; hence it can be used in the design procedure of this antenna as a serial or parallel fed array element. The computed results agree very well with measurements. The antenna attains a -3 dB gain bandwidth of 13% to 15%, a 3-dB axial ratio bandwidth of 48%, and -15 dB return loss bandwidth of 60% View full abstract»

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  • Performance analysis of antennas for hand-held transceivers using FDTD

    Page(s): 1106 - 1113
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    The design of antennas for hand-held communications devices depends on the implementation of simulation tools that can accurately model general topologies. The paper presents the analysis of small antennas mounted on hand-held transceivers using the finite-difference time-domain (FDTD) method. The key features of the FDTD implementation are discussed, with particular emphasis placed upon modeling of the source region. The technique is used to predict the gain patterns and broadband input impedance behavior of monopole, planar inverted F, and loop antenna elements mounted on the handset. Effects of the conducting handset chassis, the plastic casing around the device, and lumped elements integrated into the antenna design are illustrated. Experimental results are provided to verify the accuracy of the computational methodology. The concept of antenna diversity is discussed, and key assumptions and expressions are provided that characterize the multipath fading fields. Several computational examples demonstrate the diversity performance of two receiving antennas on a single handset View full abstract»

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  • Dielectric cover effect on rectangular microstrip antenna array

    Page(s): 1180 - 1184
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    A theoretical model to analyze a covered rectangular antenna with an arbitrary dielectric constant superstrate is developed. The antenna is simulated by the radiation of two magnetic dipoles located at the radiating edges of the patch. The Green's function of an elementary magnetic dipole in a superstrate-substrate structure, utilizing spectral-domain analysis, is formulated, and the surface-wave and radiation field are computed. An improved transmission line model, which considers the stored energy near the radiating edges and the external mutual coupling, is used to compute the input impedances and radiation efficiency. Design considerations on the superstrate thickness and its dielectric constant are discussed. Experimental data for a single element and a 4×4 microstrip array is presented to validate the theory View full abstract»

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  • A scheme for eliminating internal resonances: the parasitic body technique

    Page(s): 1089 - 1096
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    A scheme for solving ill-conditioned scattering problems associated with surface integral equations involving bodies of general composition is presented. It consists of analytically continuing a (parasitic) lossy body into the interior of a resonant geometry, where it interacts only with the resonance fields, attenuating them. The technique can be used to endow any surface code with internal resonant suppression capabilities provided it can handle, in addition to the scatterer, another lossy body or external R-sheets View full abstract»

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  • Effect of correlation between shadowing and shadowed points in rough surface scattering

    Page(s): 1154 - 1160
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    The effect of correlation between shadowing and shadowed points upon various shadowing functions is studied. The backscatter (monostatic) shadowing function for a two-dimensional perfect electric conducting surface is calculated by modifying an infinite series representation developed by Ricciardi and Sato (1983, 1986). It is shown that when correlation between all shadowing and shadowed points is neglected in the series the result reduces to one of the shadowing functions purposed by Wagner (1967). This is useful since it explains from a physical point of view one of the assumptions made by Wagner, which was necessary to obtain the closed form result. We further calculate the shadowing function with correlation included by considering the first three terms in the modified Ricciardi-Sato series. These terms provide an upper and lower bound to the exact shadowing function. We show the effect of neglecting the higher order terms by relating them to the number of intersections of the surface with the incoming rays. Finally, we present results that show that the shadowing function purposed by Smith (1967) overestimates the effect of shadowing due to the neglect of correlation between the shadowing and shadowed point and a normalization term. We also show that the shadowing function derived by Wagner, which attempts to include the effect of this correlation, does not produce an improved result View full abstract»

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  • Achievement of pencil-beam radiation from a TM01 mode circular waveguide source

    Page(s): 1188 - 1192
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    A method employing appropriately placed parallel-metallic plates in the aperture of a TM01 mode circular waveguide source so as to have it produce pencil-beam radiation is described and analyzed. Programmed computations, with experimental verification, are given for the case of a C-Band TM01 source flared out to a conical horn so as to produce moderate (22 dBi) gain. Means of extending the method to achieve higher gains (40 dBi to 60 dBi) and to modify the plate arrangement so as to produce the same effect with a TE01 mode are briefly outlined View full abstract»

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  • Rigorous analysis of three-dimensional structures incorporating dielectrics

    Page(s): 1077 - 1088
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    The paper presents the SR3D software (3D radiating structures), which calculates the electromagnetic characteristics of arbitrarily shaped structures incorporating dielectric material. The rigorous analysis method is based on the integral equation formulation. The authors included a variational approach using the reaction concept of Rumsey. The problem is numerically solved with a surface finite elements method. A guided mode excitation has been introduced in order to compute the reflection coefficient at the transmit port and the transmission coefficient between the different parts fed by guided modes. This software is validated by excellent agreement between simulated and measured radioelectric performances (patterns and SWR) View full abstract»

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IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Editor-in-Chief                                                 Kwok W. Leung