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Antennas and Propagation, IEEE Transactions on

Issue 10 • Date Oct 1992

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Displaying Results 1 - 23 of 23
  • Dual passband dichroic plate for X-band

    Page(s): 1238 - 1245
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    A need arose in the NASA Deep Space Network, a worldwide tracking system, for a dichroic plate that would be transparent at two desired frequency bands in the X-band region and be totally reflective at S-band. The dual-passband dichroic plate that was developed to meet the technical requirements is a thick metallic plate having an array of periodic round holes filled with Teflon plugs. Test results on an experimental prototype plate indicate that it is technically possible to design a dielectrically filled dichroic plate that meets all of these technical requirements View full abstract»

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  • Feeding structure contribution to radiation by patch antennas with rectangular boundaries

    Page(s): 1245 - 1249
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    A combination of piecewise sinusoidal-pulse functions and semi-infinite microstrip current expansion functions is used in the full-wave spectral-domain method to analyze microstrip antennas with arbitrary rectangular boundaries. Radiation properties are formulated in the spectral domain to achieve high numerical efficiency. Two types of microstrip antennas, edge-fed rectangular and inset fed patches, have been analyzed and measured. A line-reflect-line de-embedding algorithm has been implemented to measure the input impedance of both antennas. The results show good agreement between measurement and calculated data. The radiation patterns from the edge-fed rectangular patch are measured and are compared with the theoretical data. Results show that the current on the feed line can disturb the antenna radiation pattern View full abstract»

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  • A modal radar cross section of thin-wire targets via the singularity expansion method

    Page(s): 1256 - 1260
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    A modal radar cross section (RCS) of arbitrary wire scatterers is constructed in terms of singularity expansion method parameters. Numerical results are presented for both straight and L-shaped wire targets and are compared to computations performed in the frequency domain using the method of moments View full abstract»

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  • Continuous potential Maxwell solutions on nodal-based finite elements

    Page(s): 1192 - 1200
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    A nodal-based finite-element approach for computing electric fields in heterogeneous media is presented. The primary calculation is formulated in terms of continuous potentials, so that no special care is required on element assembly at dielectric interfaces. The resulting Galerkin weak-form matrices exhibit the special Helmholtz structure, which guarantees the absence of parasitic solutions in driven problems with physically well-posed boundary conditions. The enhanced sparsity of the Helmholtz form mitigates the extra coupling effort associated with introduction of a fourth degree of freedom relative to direct E solution. E can be extracted from the computed potentials as a postprocessing step either at nodal positions or element centroids. Solutions obtained with this approach for several benchmark and practical problems are shown to be parasite-free and essentially indistinguishable from previously reported direct E computations View full abstract»

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  • Modeling resistive strips with finite elements for TE polarization

    Page(s): 1266 - 1269
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    A formulation for modeling RF scattering from infinitely thin resistive strips is developed for TEz polarization (H-polarisation). finite-element frequency-domain approach using the Galerkin weak form and special gap elements is employed. The resistive strips can be tapered, and immersed in an arbitrary inhomogeneous dielectric/magnetic medium. This formulation has been integrated into an existing finite-element code, and results are given. These results compare well to moment-method solutions View full abstract»

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  • Application of the regularization method to the inverse black body radiation problem

    Page(s): 1249 - 1253
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    The inverse black body radiation problem is concerned with the determination of the area temperature distribution of a black body source from spectral measurements of its radiation. Although several inversion approaches have been developed, none of them has overcome the problem of ill-posedness. In this study, Tikhonov's regularization method is applied to the solution of the inverse black body radiation problem. A very simple implementation of this approach together with applications of this method are presented. The effect of the regularization parameter and operator on the results is discussed View full abstract»

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  • Incremental length diffraction coefficients for an impedance wedge

    Page(s): 1201 - 1210
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    An incremental length diffraction coefficient (ILDC) formulation is presented for the canonical problem of a locally tangent wedge with surface impedance boundary conditions on its faces. The resulting expressions are deduced in a rigorous fashion from a Sommerfeld spectral integral representation of the exact solution for the canonical wedge problem. The ILDC solution is cast into a convenient matrix form which is very simply related to the familiar geometrical theory of diffraction (GTD) expressions for the field on the Keller cone. The scattered field is decomposed into physical optics, surface wave, and fringe contributions. Most of the analysis is concerned with the fringe components; however, the particular features of the various contributions are discussed in detail View full abstract»

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  • A novel implicit time-domain boundary-integral/finite-element algorithm for computing transient electromagnetic field coupling to a metallic enclosure

    Page(s): 1155 - 1164
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    A time-domain boundary-integral/finite-element algorithm for transient electromagnetic field coupling into an enclosure (cavity) is developed. The model is based on a finite-element technique, which is coupled to the exterior region through the H-field integral equation directly in the time domain. The global electric field, throughout the interior region is driven by the tangential magnetic field over the outer surface of the enclosure. The tangential magnetic field, in turn, is related to the time-dependent incident pulsed field, and the tangential electric field over the surface of the enclosure. Hence, the electric and magnetic fields are coupled at the surface of the enclosure; the coupled equations are solved by a leap-frogging technique. Numerical based on the time-dependent finite-element/boundary-integral implicit scheme are compared with measurements. Some novel features of the newly developed algorithm are also presented View full abstract»

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  • Feed circuits of double-layered self-diplexing antenna for mobile satellite communications

    Page(s): 1269 - 1271
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    An analysis of feed circuits for a double-layered self-diplexing antenna for mobile satellite communications is presented. It is possible to reduce the weight of the diplexer for a self-diplexing antenna by getting large internal isolation between transmitting and receiving. The internal isolation is shown to be heavily dependent on the configuration and errors of the feed circuits of the antenna. The feed circuits of two- and four-point feeds for the antenna are discussed, using the cavity model of microstrip elements, and an error analysis of the feed circuit is carried out View full abstract»

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  • Frequency-dependent FDTD methods using Z transforms

    Page(s): 1223 - 1230
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    The frequency-dependent finite-difference time-domain method (FD) 2TD method has been shown to be capable of correctly calculating electromagnetic propagation through media whose dielectric properties are frequency dependent. However, as researchers search for more elaborate applications, the formulation of the (FD)2TD methods becomes more complex. In this work, the mathematics of the (FD) 2TD method is developed using Z transform theory. This has the advantages of presenting a clearer formulation, and allowing researchers to draw on the literature of systems analysis and signal processing disciplines View full abstract»

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  • Theoretical and experimental studies of the resonant frequencies of the equilateral triangular microstrip antenna

    Page(s): 1253 - 1256
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    A critical study of the resonant frequency of the equilateral triangular patch antenna is presented. The contributions include: (1) comparison of the previous experimental data of J. S. Dahele and K. F. Lee (see ibid., vol.AP-35, no.1, p.100-1, 1987) with moment method results; (2) new measurements and moment method results for εr=10.5 and comparison with Gang's hypothesis; (3) verification of the relationship among the various modes by measurements and by the moment method; and (4) a curve fitting formula yielding the resonant frequency of the lowest mode, which is within 1% of the value obtained from moment method analysis View full abstract»

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  • Design of a low sidelobe double difference beam for a circular aperture

    Page(s): 1187 - 1191
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    A low-sidelobe double-difference beam is synthesized for a circular aperture in a manner similar to the synthesis of the circular Taylor sum beam and the circular Bayliss difference beam. The method proposed allows the designer to select a peak-to-sidelobe level ratio and an integer N which controls the shape of the close-in sidelobes. Such a beam finds use in main beam ECCM applications View full abstract»

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  • A versatile wave propagation model for the VHF/UHF range considering three-dimensional terrain

    Page(s): 1121 - 1131
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    A polarimetric wave propagation model for field strength forecasting and coverage prediction in the VHF/UHF frequency range is presented. The model uses a digital terrain data bank and considers multipath propagation. Based on the uniform geometrical theory of diffraction (UTD) and physical optics an approach is described for calculating the propagation effects in natural 3-D terrain, given by topological and morphographical data. The method for field strength forecasting is described and methods for the analysis of the predicted multipath signal are discussed. It is shown how the complex probability density function (PDF) for the receiver field strength and the field strength delay spectrum can be derived. Methods for further evaluation of the transmitting channel characteristics are discussed View full abstract»

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  • Microstrip antennas and arrays on chiral substrates

    Page(s): 1260 - 1263
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    Results are presented for isolated microstrip antennas and infinite arrays of microstrip antennas printed on chiral substrates, computed from full-wave spectral domain moment method solutions. Data for resonant length, impedance, directivity, efficiency, cross-polarization level, and scan performance are compared to results obtained for a dielectric substrate of the same thickness and permittivity. It is concluded that, from the point of view of antenna characteristics, there does not seem to be any advantage to using chiral antenna substrates, while there are disadvantages in terms of increased cross-polarization levels and losses due to surface wave excitation View full abstract»

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  • Frequency-scanning grating-reflector antenna for multibeam satellite communications

    Page(s): 1231 - 1237
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    The analysis and design of a circularly polarized frequency-scanning grating-reflector antenna is presented. The antenna is intended for a multibeam satellite communication system, covering 3.1° north-south and 7.2° east-west with 25 spot beams. Frequency scanning is used for the north-south coverage, while the east-west coverage is obtained by the use of a cluster feed. The grating reflector consists of a planar frequency-scanned reflection grating with a quasi-periodic lattice geometry. The frequency-scanned grating reflects the incident field into a diffracted field composed of the first-order diffracted grating lobe. A focus-feed position for the diffracted field is obtained by a proper design of the quasi-periodic lattice geometry. Design principles for the planar grating-reflector antenna are presented together with an analysis method for predicting copolar and cross-polar radiation patterns. The analysis method is verified by experimental results View full abstract»

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  • Measurement distance effects on Bayliss difference patterns

    Page(s): 1211 - 1214
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    The effects of measurement distance in distorting low-sidelobe difference patterns are examined. Previous calculations have used obsolete suboptimum aperture distributions. The Bayliss linear distribution is a versatile, highly efficient and robust optimum distribution; its use allows a single curve of sidelobe measurement error versus measurement distance (normalized to far-field distance 2D2/λ) for a given sidelobe level. Data are given for patterns from a uniform distribution to a 50-dB Bayliss. Difference patterns require slightly larger measurement distances than sum patterns. For example, the first sidelobe of a 40-dB Bayliss pattern is in error by 1 dB at a distance of 7D2/λ. The results should apply approximately for circular apertures as well View full abstract»

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  • Performance characterization of polarimetric active radar calibrators and a new single antenna design

    Page(s): 1147 - 1154
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    Several topics associated with the use of a polarimetric active radar calibrator (PARC), which is a high radar-cross-section transponder with a known scattering matrix, are addressed. The first involves experimental measurements of the magnitudes and phases of the scattering-matrix elements of a pair of PARCs that operate at 1.25 GHz and 5.3 GHz. The measurements were conducted over a wide range of incidence angles (relative to the boresight direction) in the azimuth, elevation, 45°, and 135° planes. The 5.3-GHz PARC, which consisted of two antennas placed several wavelengths apart, exhibited symmetrical patterns with no ripples and excellent isolation between orthogonal polarization channels. The 1.25-GHz PARC, whose antennas were in very close proximity to one another, exhibited unsymmetrical patterns as well as ripples in the phase patterns, thereby introducing errors in the elements of the scattering matrix. To avoid this problem, a single-antenna PARC is designed,, using an orthomode transducer. The single-target calibration technique is extended so that it applies to the use of a PARC as well as reciprocal passive calibration devices such as spheres and trihedral corner reflectors View full abstract»

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  • A flexible optimization method for the pattern synthesis of equispaced linear arrays with equiphase excitation

    Page(s): 1113 - 1120
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    A synthesis method is proposed for linear arrays having equiphase excitation currents. In addition to allowing for the exact specification of the beamwidth and for the specification of individual sidelobe levels by index or as a function of bearing (e.g., angularly extended nulls), multiple deep narrow nulls can be specified at arbitrary bearing angles. The method is suitable for the design of broadside or endfire arrays with sum or difference patterns and can also be used for the design of superdirective arrays with good radiation efficiencies and sensitivity properties. For computational efficiency, the method uses a new constrained multivariable Remez-type L approximation technique View full abstract»

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  • Higher order absorbing boundary conditions for the finite-difference time-domain method

    Page(s): 1215 - 1222
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    Higher-order absorbing boundary conditions are introduced and implemented in a finite-difference time-domain (FDTD) computer code. Reflections caused by the absorbing boundary conditions are examined. For the case of a point source radiating in a finite computational domain, it is shown that the error decreases as the order of approximation of the absorbing boundary condition increases. Fifth-order approximation reduces the normalized reflections to less than 0.2%, whereas the widely used second-order approximation produces about 3% reflections. A method for easy implementation of any order approximation is also presented View full abstract»

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  • Propagation in a two-dimensional periodic random medium with inhomogeneous particle distribution

    Page(s): 1175 - 1186
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    The behavior of electromagnetic waves when propagating in a periodic random medium, such as a row-structured canopy, is considered. The semideterministic character of the particle distributions is represented by nonuniform extinction and phase matrices and the problem is formulated by the radiative transfer equation. Solution of the radiative transfer equation is pursued both iteratively and by using a numerical technique, based on the discrete-ordinate approximation and Taylor series expansion. It is shown that the numerical solution for the periodic canopy is computationally efficient, and a closed-form for the first-order solution (iterative approach) of the radiative transfer equation is obtained for periodic cases. The analytical and numerical results are compared with transmission measurements at L- and C-band frequencies for a corn canopy for a variety of canopy conditions, with good agreement View full abstract»

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  • Asymptotic computation of the RCS of low observable axisymmetric objects at high frequency

    Page(s): 1165 - 1174
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    A method based on high-frequency asymptotic techniques is described for rapid radar cross section (RCS) computation for arbitrary convex axisymmetric objects whose geometry is described in a computer-aided design (CAD) format. A modified version of the physical theory of diffraction (PTD), which is free from divergence problems at caustics and shadow boundaries and yields good accuracy even for low-RCS objects, is employed. The spurious contributions due to sudden truncation of the physical optics (PO) currents on the shadow boundary, which yield nonphysical results, are removed, and the accuracy of the PTD is enhanced by adding the contributions due to the creeping waves and the fringe-wave currents for discontinuities in the curvature. This modified PTD yields results that are consistent with the geometrical theory of diffraction (GTD) when the stationary phase evaluation of the fields from the induced currents is valid, and also allows the RCS to be computed for the entire range of incidence angles. The results agree well with those computed with an integral equation code View full abstract»

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  • Analysis of reflector antenna system including frequency selective surfaces

    Page(s): 1264 - 1266
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    Frequency selective surfaces (FSS) are often used in spaceborne applications of reflector antennas because of their ability to allow multiple feeds to utilize the same reflector dish. The problems inherent in evaluating the FSS separately from the reflector system are discussed. A method of integrating the FSS effects into the reflector system analysis is presented. An example is given for the proposed Advanced Tracking and Delay Relay Satellite System (ATDRSS) single-access triband reflector antenna View full abstract»

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  • Transient excitation of a straight thin-wire segment: a new look at an old problem

    Page(s): 1132 - 1146
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    The transient excitation of a straight thin-wire segment is analyzed with the aid of a one-dimensional integral equation for the current along the wire. An almost exact derivation of that equation, in which only the radial current on the end faces is approximated, is given. The integral equation obtained turns out to be identical to the reduced version of Pocklington's equation. On the basis of this derivation, existing and new numerical solution techniques are critically reviewed. Pocklington's equation and Hallen's equivalent form are solved directly by marching on in time as well as indirectly via a transformation to the frequency domain. For Pocklington's equation, a conventional moment-method discretization leads to a Toeplitz matrix that is inverted with Levinson's algorithm. For Hallen's equation, the Toeplitz structure is disturbed, and the frequency-domain constituents are determined with the aid of the conjugate-gradient-FFT method. Illustrative numerical results are presented and discussed 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