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Antennas and Propagation, IEEE Transactions on

Issue 11 • Date Nov 1989

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Displaying Results 1 - 19 of 19
  • Analysis of microstrip patch antennas using finite difference time domain method

    Page(s): 1361 - 1369
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    The study of microstrip patch antennas is directly treated in the time domain, using a modified finite-difference time-domain (FDTD) method. Assuming an appropriate choice of excitation, the frequency dependence of the relevant parameters can readily be found using the Fourier transform of the transient current. The FDTD method allows a rigorous treatment of one or several dielectric interfaces. Different types of excitation can be taken into consideration (coaxial, microstrip lines, etc.). Plotting the spatial distribution of the current density gives information about the resonance modes. The usual frequency-dependent parameters (input impedance, radiation pattern) are given for several examples View full abstract»

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  • Periodic structure ray method for analysis of coupling coefficients in large concave arrays. I. Theory

    Page(s): 1377 - 1385
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    A description is given of the periodic structure ray method (PSRM), an efficient variant of the geometric theory of diffraction (GTD) for the determination of coupling (scattering) coefficients in large arrays on concave surfaces with slowly varying curvature and/or periodicity. The method is particularly suitable for applications involving low-side-lobe lens arrays and feed-through radomes. In such arrays the coefficients of coupling between array elements can be evaluated as a superposition of a small number of contributions from the periodic structure. A typical contribution consists of a number of constituents, each expressing a specific physical process occurring during the ray's travel from the transmitting to the receiving element. The periodic structure ray formalism applies equally well to two- and three-dimensional array geometries and to a broad class of radiating elements. The final results are presented in an application-oriented form View full abstract»

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  • UTD solution for electromagnetic scattering by a circular cylinder with thin lossy coatings

    Page(s): 1463 - 1472
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    A uniform geometrical theory of diffraction (UTD) solution is obtained for the field exterior to a two-dimensional circular cylinder with a thin lossy dielectric coating. The solution is convenient for engineering applications due to its simple ray format. In the lit region, the geometrical optics (GO) solution consists of the direct incident ray and the reflected ray. In the shadow region, the geometrical theory of diffraction (GTD) uses the creeping-wave format to calculate the diffracted field. In the transition regions adjacent to the shadow boundaries, where the pure ray optical solution fails, a `universal' transition integral is used for the UTD solution to calculate the field. Numerical values for the essential transition integral are deduced, by a heuristic approach, from alternative representations of the Green's function for a circular cylinder with coating. Numerical results obtained from the UTD solution show excellent agreement with the eigenfunction results for cylinders with thin dielectric coatings View full abstract»

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  • Two numerical solutions for the parallel plate-fed slot antenna

    Page(s): 1415 - 1426
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    An integrodifferential equation for the electric field in the aperture of a parallel-plate waveguide-fed slot antenna is numerically solved using Galerkin's method, with a basis of edge-condition-weighted Chebyshev polynomials, and pulse expansion with point matching. Efficient algorithms are obtained for the elements of the reduced matrix equations for both moment methods. The numerical convergence of the techniques is demonstrated by the resultant aperture field distributions and input reflection coefficients for the case of dominant (transverse electromagnetic) mode excitation View full abstract»

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  • Surface-wave phenomena in phased slot arrays with parasitic wire arrays

    Page(s): 1398 - 1406
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    Blind spots observed in structures consisting of a slot array and parasitic straight wire arrays are investigated. Each blind spot is found to be associated with either a pattern null or the excitation of a surface wave on the corrugated structure consisting of the parasitic wires and conducting screen, with the slots shorted. The plane-wave-expansion technique is used to evaluate the coupling between arrays. It is shown analytically that for structures consisting of a single wire array, the blind spot can exist only at broadside, where there is a pattern null for the parasitic wires. For structures with two-wire arrays, such as an array of Clavin elements, a surface wave can be excited at a particular scan angle provided a certain uniformity condition in the structure is satisfied. The information presented is relevant to the incorporation of parasitic wire arrays for scan compensation View full abstract»

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  • A conjugate gradient algorithm for the treatment of multiple incident electromagnetic fields

    Page(s): 1490 - 1493
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    An iterative method based on the conjugate gradient (CG) algorithm is developed for the efficient treatment of equations involving multiple excitations. Examples show that significant time savings can be obtained as compared to treating each excitation individually with the conjugate gradient algorithm. However, these savings are not obtained without the drawback of increased memory requirements to store the additional excitations, residuals, and solutions. The efficiency of this algorithm tends to increase as additional excitations are added View full abstract»

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  • Periodic structure ray method for analysis of coupling coefficients in large concave arrays. II. Application

    Page(s): 1386 - 1397
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    For pt.I see ibid., vol.37, no.11, p.1377 (1989). The periodic structure ray method (PSRM) for evaluation of coupling coefficients in large concave array was developed in part I. The PSRM is illustrated here by an example of a circular cylindrical concave array of rectangular waveguide elements for which a modal solution also exists. Excellent agreement in amplitude and phase between the modal and the ray solutions is found. The results show that the PSRM is efficient and converges rapidly View full abstract»

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  • Scattering from composite laminate strips

    Page(s): 1427 - 1436
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    An analytical model is developed for a composite laminate consisting of unidirectional fibers embedded in a dielectric slab on a conducting strip. The physics of the problem is formulated in terms of integral equations solved by the method of moments using an entire-domain Galerkin formulation. The effect of fiber spacing, the proximity of the ground plane, and the properties of the embedding dielectric are examined in relation to the nonspecular scattering characteristics of the laminate. Results of this analysis are presented for various limiting cases and are compared with experimental data View full abstract»

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  • Design and performance of the magnetic hybrid-mode horn

    Page(s): 1407 - 1414
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    Design techniques are presented for a class of circular magnetic hybrid-mode (MHM) horns together with experimental results. In comparison with earlier techniques, this design method is simpler and more amenable to physical interpretation. The horns designed exhibit performance comparable to that of the corrugated horn except that they have an ohmic loss of 0.8 to 2.7 dB. However, it appears feasible to reduce the gain loss to less than 1 dB View full abstract»

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  • A resistive sheet approximation for mesh reflector antennas

    Page(s): 1484 - 1486
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    A simplified method of estimating the equivalent surface resistance of a reflecting mesh is presented. The equivalent resistance is obtained from the approximate mesh reflection coefficients, which are based on averaged boundary conditions. This resistance approximation allows an integral equation solution for the mesh reflector that is a simple extension of that for the perfectly conducting reflector. Paraboloid radiation patterns using physical optics in conjunction with the reflection coefficients are compared to an E-field integral equation solution for a resistive surface. The agreement is excellent for low to moderate resistance values, even in the sidelobe regions View full abstract»

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  • Cloud attenuation at millimeter wavelengths

    Page(s): 1473 - 1479
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    Total atmospheric attenuation under conditions of complete and partial cloud cover was measured at frequencies of 15 and 35 GHz in the Boston area. The attenuations were actually inferred from extinction measurements using the Sun as a source. Measurements were made at 29 elevation angles from 1° to 20°, and the angular dependence of the attenuation was examined. For most cloud conditions the attenuation was found to be proportional to the slant path distance through the absorbing atmosphere. For elevation angles above about 8°, a flat Earth approximation is valid and the slant path distance is proportional to the cosecant of the elevation angle. For low elevation angles the slant path distance is a function of the effective earth radius and the effective height of the attenuating atmosphere, in addition to the elevation angle. A statistical technique for determining the radius and height is described. A zenith attenuation was extrapolated from each set of data. The humidity and frequency dependence of the attenuation was examined. An algorithm for estimating total atmospheric attenuation as a function of elevation angle, frequency, and surface absolute humidity was derived View full abstract»

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  • An experimental and theoretical study of self-phased arrays in mobile satellite communications

    Page(s): 1370 - 1376
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    Communication with satellites from ships and aircraft requires the accurate pointing of a high-gain antenna. The self-phased array, which performs beam steering automatically by the use of a pilot carrier, offers a number of advantages in this application. The principles and properties of this type of array are outlined, and their implications for array design are discussed. An experimental self-phased system using a phase-locked loop, which receives signals from the Marecs satellite over the Atlantic Ocean, is described. Results are presented for a two-element laboratory prototype to illustrate its performance. The behavior of the self-phased-array concept under multipath conditions is particularly interesting and is examined both theoretically and experimentally View full abstract»

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  • An impedance-matching technique for increasing the bandwidth of microstrip antennas

    Page(s): 1345 - 1354
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    The nature of the inherent narrow bandwidth of conventional microstrip patch antennas is considered. It is observed that, except for single-feed circularly polarized elements, their bandwidth is limited only by the resonant behavior of the input impedance and not by radiation pattern or gain variations, which usually are negligible over a moderate 10 to 20% bandwidth. Therefore, broadband impedance matching is proposed as a natural to increase the bandwidth. The maximum obtainable bandwidth is calculated using Fano's broadband matching theory. It is found that by using an optimally designed impedance-matching network, the bandwidth can be increased by a factor of at least 3.9, the exact value depending on the degree of matching required. A transmission-line prototype for a proper matching network is developed. The translation of this prototype network into a practical structure (e.g. a microstrip or stripline circuit) is considered. Practical design examples and experimental results which clearly show the validity of the technique are given View full abstract»

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  • H-polarization diffraction by a thick metal-dielectric join

    Page(s): 1453 - 1462
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    An analysis is presented of the H-polarization diffraction due to a material discontinuity formed by the junction of a thick dielectric half-plane with a metallic half-plane having the same thickness. This is accomplished by first considering the solution of several subproblems. These include the direct diffraction and coupling due to a plane wave incident on a loaded open-ended parallel plate waveguide and radiation and reflection by a waveguide mode. The final solution for diffraction by the metal-dielectric join is obtained by introducing a perfectly conducting stub within the loaded guide and subsequently using the generalized scattering matrix formulation with the stub brought to the waveguide opening. All the analysis relating to the subproblems is done by the dual integral equation approach. As expected, the final expressions involve several Wiener-Hopf split functions which are evaluated numerically or analytically View full abstract»

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  • Cosine pattern synthesis for single and multiple main beam uniformly spaced linear arrays

    Page(s): 1480 - 1484
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    The method of cosine pattern synthesis for single- and multiple-main-beam equispaced linear arrays is introduced. The cosine pattern function is characterized by the position of the main beam in the θ-domain and its half-power beamwidth. The Fourier series and Woodward-Lawson methods are applied to the special cases of single- or multiple-main-beam cosine pattern synthesis. The patterns produced by application of these classical shaped-beam synthesis methods can then be used as initial patterns for iterative and perturbational techniques. Examples are presented and discussed, including the use of multiple-main-beam cosine pattern synthesis to design a high-power, high-frequency, ground-based transmitter for the creation of an array of `wireless' ionospheric dipoles View full abstract»

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  • Periodic chiral structures

    Page(s): 1447 - 1452
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    The electromagnetic properties of a structure that is both chiral and periodic are investigated using coupled-mode equations. The chirality is characterized by the constitutive relations DE+iξcB and H=iξcE+B/μ, where ξc is the chiral admittance. The periodicity is described by a sinusoidal perturbation of the permittivity, permeability, and chiral admittance. The coupled-mode equations are derived from physical considerations and used to examine bandgap structure and reflected and transmitted fields. Chirality is observed predominantly in transmission, whereas periodicity is present in both reflection and transmission View full abstract»

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  • Analysis of finite phased arrays of circular microstrip patches

    Page(s): 1355 - 1360
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    A method is presented for analyzing a finite planar array of circular microstrip patches fed by coaxial probes. The self- and mutual impedances between array elements are calculated using the method of moments with the dyadic Green's function for a dielectric layer on a ground plane. The patch circuits are determined by using the reaction integral equation. The active input impedance as well as the active element pattern of the array are computed from a knowledge of the resultant patch currents. The calculated results for two-element and eight-element linear arrays are in good agreement with experimental data. The active reflection coefficient and element pattern for the center and edge elements of a two-dimensional array as a function of scan angle are also presented View full abstract»

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  • Analysis of two-dimensional electromagnetic scattering from nonplanar periodic surfaces using a strip current model

    Page(s): 1437 - 1446
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    A method-of-moments solution is presented for the problem of two-dimensional transverse magnetic (TM) scattering of a plane wave from a nonplanar periodic surface separating two contrasting homogeneous media. The moment solution uses fictitious spatially periodic and properly modulated electric current strips to simulate the field scattered by the surface and the field penetrating the surface. The fields radiated by the current strips are represented in terms of Floquet modes, and the problem is reduced to a consideration of the fields over a single period. The simulated fields are forced to obey the continuity conditions for the tangential components of the electric and magnetic fields at a selected set of points on the interface within a single period. The procedure is simple to implement, rapidly converging, and applicable to arbitrary smooth profiles. Perfectly conducting media are treated as reduced cases of the general procedure for penetrable media. Results for sinusoidal surfaces are given and compared with available data. The efficiency of the method is demonstrated View full abstract»

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  • Improvement of the numerical solution of dielectric bodies with high permittivity

    Page(s): 1486 - 1490
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    A method for improving the accuracy of the numerical solution of dielectric bodies is presented. Its utilization makes the matrix size independent of the relative dielectric constant and reduces its size. It also improves the accuracy of the solution of the Muller formulation when the dielectric constant is high. The root-mean-square (RMS) errors are calculated for dielectric spheres by comparing the numerical solution with the exact solution using Mei series. The magnitude and phase of the surface current distributions are presented. The bistatic radar cross sections of the sphere and finite cylinder, obtained by different formulations, are presented 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