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Antennas and Propagation, IEEE Transactions on

Issue 10 • Date Oct. 1988

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Displaying Results 1 - 25 of 25
  • Comments, with reply, on "A generalization of Van den Berg's integral-square error computational technique for scattering" by A.J. Mackay and A. McCowen

    Publication Year: 1988 , Page(s): 1497 - 1498
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    The commenters note that if the conjugate gradient method were used in the above named work (ibid., vol.AP-35, p.213-20, Feb. 1987) its use automatically enforces the orthogonality of the authors' functions, without requiring any additional storage. In replying the authors agree that it was perhaps an oversight not to compare Van den Berg's method with the conjugate gradient method. However, they note that it was not their aim to provide such a comparison, but only to show how improvements could be made to the spectral iteration technique (SIT).<> View full abstract»

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  • A comparison of experimental and theoretical values of atmospheric absorption at the longer millimeter wavelengths

    Publication Year: 1988 , Page(s): 1471 - 1480
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    Results of atmospheric absorption measurements made over very long slant paths at frequencies of 15 and 35 GHz are reported. The absorption was determined from a set of measurements using the Sun as a source. Fifty-eight sets of data were collected at sunrise and sunset during clear sky conditions for a set of elevation angles from near the horizon to 20°. The surface absorption coefficient, zenith absorption, and effective height of the absorbing atmosphere were derived from these data. Regressions of both surface absorption coefficient and zenith absorption were performed as a function of surface absolute humidity; the results were compared with theoretical values obtained by several investigators. Zenith absorptions were found to be in good agreement with theory. However, experimental surface absorption coefficients were consistently lower than the calculated values View full abstract»

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  • Antenna reflector metrology: the Australia Telescope experience

    Publication Year: 1988 , Page(s): 1481 - 1484
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    A description is given of some refinements to the traditional theodolite and tape technique for surveying the reflector surface of large antennas. The theodolite is positioned in the structural axis about 40 cm above the antenna vertex. There are six rings of panels, ranging in size from 1.4 m×0.7 m to 2 m×2 m, with 160 panels in all in each antenna. Targets are placed near the corners of each panel. In brief, each target's position is defined by two measurements: its distance from the theodolite, and the angle between the antenna axis and the line of sight to target, the zenith angle. The equipment and the procedures used are reported. The authors examine the accuracy achieved in each measurement and discuss the consequent panel positional accuracy. In applications (to radio telescope antennas 18-m and 22-m in diameter), surface accuracies of 0.25 mm root mean square (RMS) have been achieved View full abstract»

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  • A simple algorithm for sidelobe cancellation in a partially adaptive linear array

    Publication Year: 1988 , Page(s): 1482 - 1486
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    It is argues that the far-field lobes of the edge elements of a uniformly excited linear array are nearly equal to the sidelobes of the array itself, and hence the edge elements are ideal for cancellation of specific sidelobes of the pattern. This supports the concept of partial adaptivity using only the edge elements. This technique is suitable for real-time implementation because only the edge elements require direct control; the inner elements are controlled by programmable read-only memories. Other advantages reported are: the nulls produced specifically by control of the edge elements are deep and wide, and the main-beam gain is not much affected by the sidelobe cancellation View full abstract»

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  • A note on hybrid finite element method for solving scattering problems

    Publication Year: 1988 , Page(s): 1486 - 1490
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The hybrid finite-element formulation (HFEM) originated by P. Silvester and M.S. Hsieh (1971) is modified in such a way that it results in a sparse or uniformly banded matrix, rather than a partly full and partly sparse nonuniform matrix. The modification is accomplished by changing the sequence of matrix substitutions and substantially improves the computational efficiency and enhances the capability of the method, which is demonstrated by numerical examples. A comparison with other numerical techniques is presented View full abstract»

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  • An asymptotic high-frequency analysis of the radiation by a source on a perfectly conducting convex cylinder with an impedance surface patch [antennas]

    Publication Year: 1988 , Page(s): 1407 - 1417
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (860 KB)  

    A high-frequency approximation is presented for the fields radiated by a magnetic line or line dipole source which is located on an impedance surface patch that partly covers an electrically large, perfectly conducting convex cylinder. Relatively simple asymptotic approximations are developed for the currents induced on the impedance surface by the line sources, and the radiation patterns are calculated by incorporating these surface currents into the radiation integral. The latter integral exists only over the patch region as it uses a perfectly conducting cylinder Green's function which is expressed in terms of a uniform geometrical diffraction (UTD) solution. Numerical results are presented and shown to compare very well with other independent calculations and measurements View full abstract»

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  • The effects of the thermal protection system on the Space Shuttle S-band quad antennas

    Publication Year: 1988 , Page(s): 1389 - 1395
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    A theory is presented to determine the effects of the multiple dielectric thermal protection system on the Space Shuttle orbiter's S-band quad antennas. A ray optics approach is developed which indicates internal reflections from the orbiter metallic skin and multiple dielectric layers. The results of the computer program developed show that the beamwidth of the two upper quad antennas is narrowed by a thermal protection system. The results also show that the thermal protection system will cause significant depolarization of a circularly polarized signal as the angle from the normal to the antenna surface is increased. Heating of the thermal protection surface or degradation due to multiple missions may also be predicted by incorporating changes in the complex permittivity as a function of temperature. Heating and multiple mission effects are found to be less than 1 dB View full abstract»

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  • Backfire radiation from a monofilar helix with a small ground plane

    Publication Year: 1988 , Page(s): 1359 - 1364
    Cited by:  Papers (18)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    Numerical analysis of a helical antenna is made in the presence of a finite-grid ground plane. It is found that the transition from forward-fire radiation to backfire radiation occurs as the ground-plane diameter is reduced to the order of the helix diameter. The investigation of the backfire helix with a small ground plane shows that a circularly polarized wave is radiated over a frequency range of more than 1 to 1.3. An application of the backfire helix to primary feed for a paraboloidal reflector is also described, in which the far-field pattern is evaluated by the physical-optics approximation View full abstract»

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  • A piecewise deformable subreflector for compensation of Cassegrain main reflector errors

    Publication Year: 1988 , Page(s): 1343 - 1350
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    The subreflector presented is built of an aggregate of rigid panels, which are controlled by a small number of actuators. An algorithm is described to calculate the actuator motions for a set of given surface distortions. It is assumed that the surface distortions, at different elevation angles, are known a priori. Geometrical optics is used to describe the aperture field distribution and to predict the improvement in performance. Computer modeling of main and subreflectors was used to test the design. This design is suggested for the improvement of a hypothetical radio telescope. In this example, it is predicted that the effective surface errors, due to gravitational distortions, may be reduced to 33% of their uncorrected level with a 48-plate subreflector. Compensation with other subreflector configurations is also investigated View full abstract»

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  • RCS measurement of small circular holes

    Publication Year: 1988 , Page(s): 1495 - 1497
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    The Rayleigh scattering from small circular holes in a thin screen was studied. The backscattered fields calculated from a dipole expansion were compared those from an exact solution and measurements for a single, electrically small hole. The backscatter from the holes is given by rather simple expansion where the first term is adequate for a good engineering solution. These expressions are within 1 dB of the exact solution for ka⩽0.96 for E-plane scattering and ka⩽0.69 for H-plane scattering when a is the hole's radius and k is the propagation constant View full abstract»

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  • Circular array of outward sloping monopoles for vehicular diversity antennas

    Publication Year: 1988 , Page(s): 1365 - 1374
    Cited by:  Papers (9)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    A circular array of outward-sloping monopoles is analyzed as a diversity antenna for vehicle rooftop mounting. The monopoles are assumed to approximate minimum scattering antennas, have sinusoidal current distributions, and reside on an infinite, perfectly conducting ground plane. The envelopes of the received signals are considered Rayleigh distributed. The advantage of the array configuration is that the feedpoint spacing can be made almost arbitrarily small, even for a large number of branches. A three-element array with element lengths of 0.6 wavelengths and feedpoint spacing 0.1 wavelengths operating at 463 MHz was field-tested and the results are in good agreement with the analysis View full abstract»

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  • Integrals for the mutual coupling between dipoles or between slots: with or without complex conjugate?

    Publication Year: 1988 , Page(s): 1375 - 1381
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    Derivations are given for two integral expressions that give the mutual impedance between dipoles, and a comparison is made. This leads to the conclusion that the expression without the complex conjugate, based on reciprocity, has to be preferred. The expression with complex conjugate, the induced-electromotive-force (EMF) method, is not exact. For practical purposes, however, both are often equivalent. For the mutual admittance between slots in a conducting ground plane, or magnetic currents, the conclusions are reversed: the induced-EMF method is the preferred one, while the reciprocity method is only valid for purely real slot excitations or current distributions View full abstract»

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  • TE/TM decomposition of electromagnetic sources

    Publication Year: 1988 , Page(s): 1382 - 1388
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    Three methods are given by which bounded electromagnetic sources can be decomposed into two parts radiating transverse electric (TE) and transverse magnetic (TM) fields with respect to a given constant direction in space. The theory applies source equivalence and nonradiating source concepts, which lead to decomposition methods based on a recursive formula or two differential equations for the determination of the TE and TM components of the original source. Decompositions for a dipole in terms of point, line, and plane sources are studied in detail. As an application of the point decomposition method, it is demonstrated that the general exact image expression for the Sommerfold half-space problem, previously derived through heuristic reasoning, can be more straightforwardly obtained through the decomposition method View full abstract»

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  • Array feed synthesis for correction of reflector distortion and vernier beamsteering

    Publication Year: 1988 , Page(s): 1351 - 1358
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    An algorithmic procedure is described for the synthesis of a planar-array for paraboloidal reflectors to provide simultaneously electronic correction of systematic reflector surface distortions as well as a vernier electronic beamsteering capability. Several f/D ratios and distortion models were examined that are typical of large paraboloidal reflectors. Numerical results are presented showing that, for the range of distortion models considered, significant on-axis gain restoration can be achieved with a one-ring (seven-element) array. However, with seven elements, the array parameters that maximize system gain, do not provide uniform beam-steering (±1 BW) and an additional ring (19 elements) is required. For arrays either 7 or 19 elements, the results indicate that the use of high-aperture-efficiency elements in the array yields higher system gain than can be obtained with elements having lower aperture efficiency. Contour plots of the focal-plane fields are also presented for various distortion and beam-scan-angle cases, showing the dynamic nature of the problem View full abstract»

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  • On a surface integral representation for homogeneous anisotropic regions: two-dimensional case

    Publication Year: 1988 , Page(s): 1401 - 1406
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    A mathematical statement of the Huygen's principle for an electromagnetic field in an anisotropic region is obtained by a linear mapping of the original anisotropic region into a complex isotropic region using the material permeability and permittivity tensors. The original field equations are reduced to canonical form so that they resemble Helmholtz equations in transform space. This allows the use Huygen's principle in the transform space, after which the result is mapped back into real space; here the resulting contour quantities can be expressed in terms of tangential field quantities, using Maxwell's equations. The field representation is found to be polarization-dependent. In this two-dimensional analysis, each polarization has a different representation and is therefore treated both separately and using duality. Some elementary applications to scattering are presented and discussed in detail View full abstract»

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  • Symbolic code approach to GTD ray tracing

    Publication Year: 1988 , Page(s): 1492 - 1495
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    A high-level artificial intelligence language with symbolic/logical manipulation capabilities, together with a simple ansatz based on the properties of the Fresnel ellipsoid, is used to implement an efficient computer algorithm for automatic ray-tracing. The geometrical theory of diffraction (GTD) ray-tracing solution for the radio-line path-loss evaluation over piecewise-linear two-dimensional terrain profiles is presented View full abstract»

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  • Reflection properties of the Salisbury screen

    Publication Year: 1988 , Page(s): 1443 - 1454
    Cited by:  Papers (103)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    The reflection properties of multiple electric/magnetic Salisbury screens have been studied. Analytical formulae are developed for the maximally flat design of two- and three-screen planar stackups that have taken into account appropriate values for the spacer materials used to separate the screens. The effect of curvature has also been assessed. It is shown that relatively large reductions in specular reflection are possible over sizeable bandwidths using relatively few Salisbury screens. Furthermore, these reductions are not completely destroyed if the incident wave is not normal to the surface, if the surface is curved or if there are errors in fabrication of the screen View full abstract»

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  • The determination of the propagation constant for the traveling wave in an infinite ground plane

    Publication Year: 1988 , Page(s): 1455 - 1463
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    The propagation constant for the travelling wave in a trough in an infinite ground plane is examined. The null-field integral is used to determine the electromagnetic field in the trough structure, and pulse basis functions give the distribution of the aperture fields. From this, the propagation constant is solved for, using the Newton-Raphson iterative scheme. Various sizes of geometries are examined. The far-field patterns are calculated and compared with other solutions, thereby validating the integral formulation which subsequently provided the propagation constant. Measurements of two trough geometries are performed to validate the theoretical results View full abstract»

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  • Modeling electromagnetic wave propagation in the troposphere using the parabolic equation

    Publication Year: 1988 , Page(s): 1464 - 1470
    Cited by:  Papers (64)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A computational method is described for predicting electromagnetic wave propagation in the troposphere using the parabolic approximation of the Helmholtz wave equation. The model represents propagation over a spherical, finitely conducting Earth and allows specification of frequency, polarization, antenna pattern, antenna altitude, and elevation angle. The method enables calculations to be performed using either ideal or measured refractivity profiles that vary in both altitude and range. A brief discussion of the theoretical formulation and computational implementation of the propagation model is presented, followed by examples that demonstrate various features. Example calculations include 3-GHz propagation over a calm sea in the presence of both range-dependent and range-independent surface-based ducts as well as in standard atmosphere conditions. Comparisons with two other propagation models are also discussed View full abstract»

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  • The conjugate gradient spectral iterative technique for planar structures

    Publication Year: 1988 , Page(s): 1418 - 1423
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    It is shown that using the spectral iterative technique (SIT) to solve the first-kind integral equation is equivalent to the Neumann iterative solution of a related second-kind integral equation. It is thus shown that SIT only converges when the norm of the operator in the second-kind equation is small enough. Applying a conjugate gradient technique to the second-kind equation results in a convergent iterative scheme. Some representative numerical results show a superiority in the rate of convergence of the conjugate gradient scheme for the second-kind equation (CGSIT-scheme) when compared with the convergence of the conjugate scheme for the original first-kind equation (CG-scheme). The CGSIT-scheme combines the advantages of the conjugate gradient method with those of the spectral iterative technique View full abstract»

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  • Infinite elements and base functions for rotationally symmetric electromagnetic waves

    Publication Year: 1988 , Page(s): 1490 - 1491
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB)  

    The finite-element method is applicable to infinite domains if the outermost `finite' elements are infinite and their base functions satisfy the boundary conditions at infinity. Appropriate infinite elements fitted to triangular or quadratic finite-element net and corresponding base functions satisfying Sommerfield's radiation condition of electromagnetic waves are introduced. The application of the defined infinite elements is illustrated for the problem of the radiation of a coaxial cable to a half-space. The results are in very good agreement with those found in the literature View full abstract»

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  • The null field approach to electromagnetic scattering from composite objects: the case with three or more constituents

    Publication Year: 1988 , Page(s): 1396 - 1400
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    A null-field approach to scattering from composite objects due to S. Strom and W. Zhengs (ibid., vol.36, no.3, p.376-82, 1988) is extended to scatterers consisting of three of more homogeneous parts. The numerical performance of this extension has been tested for a number of different types of scatterers, and the numerical results have been compared with other computed and measured results. In particular, the application of the extended formulation to scattering from elongated objects is described and illustrated by numerical computations View full abstract»

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  • Scattering from stacked gratings and dielectrics for various angles of wave incidence

    Publication Year: 1988 , Page(s): 1435 - 1442
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    The theory of scattering matrices and microwave network analysis is used to solve the problem of scattering from cascaded infinite periodic gratings. The total reflection and transmission coefficients are calculated as functions of angle of incidence, wire spacing for each grating separation, wire thickness, and number of gratings that comprise the cascaded structure. The problem of stacking dielectric slabs with periodic gratings is also formulated and solved. In all cases, the secant corrector spectral iteration approach is used as a numerical method for calculating the desired currents and fields. Finally, the calculated values of the reflection and transmission coefficients are presented and compared with reported experimental and theoretical data View full abstract»

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  • Multiport network model and transmission characteristics of two-port rectangular microstrip patch antennas

    Publication Year: 1988 , Page(s): 1337 - 1342
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    A multiport network model for two-port rectangular microstrip patch antennas is introduced. This model is capable of accounting for the feedline-patch junction reactances as well as for the mutual coupling among the edges of the patch, and is used to evaluate two-port transmission characteristics of rectangular patches. The proposed model has been applied to the analysis of rectangular patches used as elements of series-fed microstrip arrays. Results presented show that it is possible to match a two-port patch at the input port and, at the same time, to achieve a specified transmission coefficient to the other port to taper the amplitude distribution of the array appropriately. These experimental results verify the validity of the proposed model and the method of analysis used View full abstract»

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  • Diffraction of a plane wave by an inclined parallel plate grating

    Publication Year: 1988 , Page(s): 1424 - 1434
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The diffraction of a plane electromagnetic wave by an inclined parallel plate grating is treated by using the Weiner-Hopf technique. The problem is formulated in terms of the single Wiener-Hopf equation, which is then using a factorization and decomposition procedure. The solution is exact but formal in the sense that there is an infinite number of unknowns. Approximation procedures are presented and two forms of the approximate solution are derived. Based on the above analysis, numerical examples are given and the transmission characteristics of the grating are 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