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Antennas and Propagation, IEEE Transactions on

Issue 10 • Date October 1984

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Displaying Results 1 - 25 of 27
  • [Front cover and table of contents]

    Publication Year: 1984 , Page(s): 0
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    Freely Available from IEEE
  • Comments on "Plane-wave diffraction by a wedge - A spectral domain approach

    Publication Year: 1984 , Page(s): 1141 - 1142
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    First Page of the Article
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  • Comments on "Synthesis of offset dual shaped subreflector antennas for control of Cassegrain aperture distributions"

    Publication Year: 1984 , Page(s): 1142 - 1145
    Cited by:  Papers (4)
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    In the paper by V. Galindo-Israel and R. Mittra it is claimed that a dual shaped subreflector (DSS) feed can be used to upgrade the efficiency of classical Cassegrain antennas. In this comment it is shown that upgrading is not possible unless the diameter of the DSS feed is extremely large. In fact, if the Cassegrain antenna at Goldstone, CA, used as an example in the above paper, is fed by the DSS feed, the efficiency in X -band will be about the same as or less than if it is fed directly by an optimized scalar horn. The low efficiency is caused by diffraction. Instead, the efficiency can be upgraded by using a scalar horn with shaped lens. View full abstract»

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  • [Back cover]

    Publication Year: 1984 , Page(s): c4
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    Freely Available from IEEE
  • Electronic scanning by ferrite-loaded corner reflector antennas

    Publication Year: 1984 , Page(s): 1013 - 1017
    Cited by:  Papers (3)
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    The measured performances of the antennas which consist of a 90\deg corner reflector, a horn, a core wire of a coaxial line, two or three ferrite rods, and electromagnets magnetizing the respective ferrites are presented. The following are made clear for the antenna with two ferrite rods. The load of the ferrites yields the asymmetric power pattern owing to the anisotropy of the ferrites, though the antenna geometry and the magnetization of the ferrites are symmetric. Moreover, the remarkably sharper main lobe and the higher gain are obtained by loading the ferrites. The main lobe can be turned to the direction reflected about the symmetric plane of the antenna by reversing all the dc magnetic fields applied to the ferrites, that is, electronic lobe switching in the H -plane is realized. It is shown that the antenna loaded with three ferrite rods makes the continuous scan of the main lobe possible by applying the suitable magnetic fields to the ferrites. The direction of the main lobe of these antennas is turned by electronically changing the currents of the electromagnets, that is, by changing the tensor permeabilities of the ferrites. The reciprocity for antennas composed of isotropic media does not hold for these antennas. The receiving power pattern coincides with the transmitting pattern reflected about the symmetric plane when the same dc magnetic fields are applied for both cases. Hence, these antennas permit us to receive from a direction and simultaneously to transmit in the direction reflected about the symmetric plane. View full abstract»

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  • Diffraction corrections to the cylindrical wave radiated by a linear array feed of a cylindrical reflector antenna

    Publication Year: 1984 , Page(s): 1111 - 1116
    Cited by:  Papers (8)
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    A phase-steered linear array feed for a parabolic cylindrical reflector antenna is considered. The nearly cylindrical wave radiated from this line feed in the Fresnel zone is expressed in terms of the isolated-element pattern. The correction to this wave due to diffraction from the endpoints of the line feed and from the grating formed by the array elements is also derived. View full abstract»

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  • A backfire helical feed

    Publication Year: 1984 , Page(s): 1126 - 1128
    Cited by:  Papers (3)
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    A novel backfire helical feed for a paraboloidal reflector is described. The antenna requirements were a 20 percent bandwidth at L - band, right-hand circular polarization, a maximum voltage standing-wave ratio (VSWR) of 2.0, and a peak power capability of 200 kW unpressurized. The feed consists basically of a 3.5-turn helix wound around a 1frac{5}{8} -in rigid coaxial transmission line. The 50 \Omega transmission line is coupled to the helix through a two-stage transformer within the coax followed by a half-wave coax to two-wire (unequal diameters) balun. View full abstract»

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  • Iterative computational techniques in scattering based upon the integrated square error criterion

    Publication Year: 1984 , Page(s): 1063 - 1071
    Cited by:  Papers (72)  |  Patents (2)
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    An iterative technique is developed to rigorously compute the electromagnetic time- and frequency-domain scattering problems. The method is based upon a wave-function expansion technique (this also includes the integral-representation techniques), in which the electromagnetic field equations and causality conditions are satisfied analytically, while the boundary conditions or the constitutive relations have to be satisfied in a computational manner. The latter is accomplished by an iterative minimization of the integrated square error. For the solution of an integral equation, it is shown how to obtain optimum convergence. Some numerical results pertaining to a number of representative problems illustrate the numerical advantages and disadvantages of the iterative method. View full abstract»

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  • A note on the relation between slot conductance and slot voltage

    Publication Year: 1984 , Page(s): 1133 - 1134
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    First Page of the Article
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  • Radar cross section of long wires

    Publication Year: 1984 , Page(s): 1124 - 1126
    Cited by:  Papers (2)
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    Using a continuous wave (CW) Doppler radar at 60 GHz, the radar cross sections of long metallic rods were measured. The results show linear increase with growing distance between radar and rods. A new expression for the radar cross section, which was also derived, demonstrates good agreement with the measured data. View full abstract»

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  • Relation between the ringing of resonances and surface waves in radar scattering

    Publication Year: 1984 , Page(s): 1071 - 1079
    Cited by:  Papers (7)
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    The exact normal-mode or Mie series for electromagnetic scattering from a conducting sphere has in the previous literature been transformed via the Watson transformation into components corresponding to specularly reflected and to creeping waves, or via the singularity expansion method (SEM) into a series of pole contributions in the complex frequency plane which in the time domain give rise to a series of damped sinusoidal signals. In this work, the connection between the two methods is established by using the Watson transformation for obtaining the specular wave, and by transforming the remainder into the SEM series. From the latter, we obtain the shapes of creeping-wave pulses for the case of an incident \delta -function pulse by evaluating the series via the stationary-phase method. View full abstract»

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  • A compact Q-K-band dual frequency feed horn

    Publication Year: 1984 , Page(s): 1108 - 1111
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    A millimeter-wave dual frequency circularly polarized feed for an offset reflector antenna is being developed for a portable satellite ground terminal. The two frequency bands are Q - and K -bands for transmit and receive, respectively. A compact feed design consisting of a single corrugated horn with two circular waveguide concentric openings at the horn throat is described. Good aperture efficiency and low sidelobes in both of the frequency bands are achieved. View full abstract»

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  • Microwave holographic imaging method with improved resolution

    Publication Year: 1984 , Page(s): 1018 - 1026
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    A multifrequency holographic microwave imaging method with high resolving capability in both azimuth and range directions, is described. The method incorporates a synthetic aperture approach in pulse radar systems, originally designed for the pulse-echo imaging, in order to improve azimuth resolution. The imaging technique places no constraint on the waveform of a transmitted signal in use and allows the three-dimensional imaging. This paper develops 1) the general formula, which describes the relation between the transmitted and received signals, based on Kirchhoff diffraction theory, 2) a test function, which is the kernel of a linear operation for producing object images from received signals, and 3) a filter design technique for compressing the durations and suppressing the sidelobe levels of received signals. Numerical image reconstructions are presented for demonstrating high resolution capability of the method. View full abstract»

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  • Modeling antennas near to and penetrating a lossy interface

    Publication Year: 1984 , Page(s): 1040 - 1049
    Cited by:  Papers (55)
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    A technique for modeling wire objects interacting across or penetrating the planar interface which separates two half-spaces is described. The moment-method treatment is employed, based on the thin wire approximation to the electric-field integral equation, with the effect of the interface included via the Sommerfeld integrals. The computation time associated with evaluating the latter is substantially shortened by using an interpolation-based technique plus asymptotic field expressions. Although developed specifically for the wire problem, the procedure is also applicable, with slight modification, to modeling surface objects as well. Special care is taken to account for the charge discontinuity that occurs at the point a wire penetrates the interface. Example calculations are shown for a monopole antenna driven against ground stakes and simple ground screens, the fields of buried objects, and a simple electromagnetic pulse (EMP) simulator. View full abstract»

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  • Scalar horn with shaped lens improves Cassegrain efficiency

    Publication Year: 1984 , Page(s): 1094 - 1100
    Cited by:  Papers (11)  |  Patents (4)
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    It is shown that the aperture efficiency of a classical Cassegrain antenna can be considerably improved if the radiation pattern of the feed is optimally shaped. The corresponding optimum field distribution Over the aperture of the feed consists of a circular main lobe which is surrounded by concentric sidelobe rings. This optimum field distribution with one sidelobe ring included is realized by shaping of a dielectric lens which is positioned in the aperture of a corrugated horn antenna. The design can provide a theoretical aperture efficiency of 90.5 percent when subreflector diffraction and aperture shadowing are neglected, i.e., an improvement of 0.4 dB compared to an optimum conventional feed. Measurements of a model at 22.8 GHz gave a practical result of 85.6 percent. If the model is used to feed a 30 m radiotelescope the overall antenna efficiency becomes about 71 percent. View full abstract»

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  • Amplitude distribution of composite terrain radar clutter and the κ-Distribution

    Publication Year: 1984 , Page(s): 1049 - 1062
    Cited by:  Papers (78)  |  Patents (1)
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    A novel class of probability distributions resulting from a compound Poisson process is found to correlate well with amplitude distributions of radar clutter returns spatially sampled from composite terrain. This class of distributions, derived from assumptions of random scattering phase and Poisson spatial distribution of elementary scattering sources, is specified by several physical and statistical parameters in its complete generality. These parameters are: 1) the number of scatterer types; 2) the average radar scattering cross section and the cross-sectional distribution of each different scatterer type; 3) the occurrence probability or the average scatterer size and spatial density; 4) the radar resolution area; and 5) the average background radiation as well as the radar internal noise power. Excellent fits of the theoretical clutter distributions to the measurement data are obtained by assuming a Rayleigh amplitude distribution for the elementary scatterer return for high grazing angle cases and a more general K -distribution for low grazing angle cases. View full abstract»

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  • Taylor patterns for discrete arrays

    Publication Year: 1984 , Page(s): 1089 - 1093
    Cited by:  Papers (55)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    The equivalent of a Taylor pattern for continuous apertures is developed for discrete arrays. This array factor can be realized exactly, since it belongs to the appropriate class of patterns. A method for determining the element excitations is also presented. As an example, the pattern and excitations are calculated for a 41-element array with \bar{n} = 6 and a 25 dB design sidelobe level. Comparison is made with the patterns obtained by applying root matching and sampling of a continuous Taylor aperture. View full abstract»

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  • Design of wide-band compact corrugated horns

    Publication Year: 1984 , Page(s): 1134 - 1138
    Cited by:  Papers (32)
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    It is shown that a specially profiled corrugated horn with a ring-loaded input converter section is capable of operating over bandwidth ratios of up to 2.4: 1. The cross polarization across the band is relatively low, and the change in beamwidth and phase-center position with frequency is acceptable for many applications. This "compact" horn is significantly smaller than the conventional wide-band corrugated horn, and is particularly recommended as a feed in a dual-reflector antenna where space is limited. View full abstract»

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  • A uniform asymptotic expansion of a typical diffraction integral with many coalescing simple pole singularities and a first-order saddle point

    Publication Year: 1984 , Page(s): 1122 - 1124
    Cited by:  Papers (18)
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    The asymptotic evaluation of a typical diffraction integral with many coalescing simple pole singularities and a first-order saddle point is examined. A uniform solution is obtained by means of the Taylor expansion. View full abstract»

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  • Transient response computation of spheroidal objects using impedance boundary conditions

    Publication Year: 1984 , Page(s): 1116 - 1122
    Cited by:  Papers (1)
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    The transient response of imperfectly conducting and permeable spheroidal objects is determined using the impedance boundary conditions. Since the impedance boundary conditions are not known in the time domain, the frequency domain analysis is used to formulate the problem. The use of impedance boundary conditions relates conveniently the solution to the object's physical parameters and simplifies the computations. For highly conducting objects a simplified method is used to determine numerically the frequency domain data, which utilizes the numerical code for perfectly conducting objects. The excitation is assumed to be due to a periodic pulse train and generated by a small circular loop antenna. The procedure for the computation of the transient response, at very low excitation frequencies, is presented and the response forms for different object parameters and orientations are computed. View full abstract»

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  • A new technique for shaped beam synthesis of equispaced arrays

    Publication Year: 1984 , Page(s): 1129 - 1133
    Cited by:  Papers (37)
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    Use is made of an existing technique to synthesize a sum pattern whose sidelobe peaks fit a prescribed envelope in a specified segment of the visible region. In terms of a polynomial representation of the pattern, certain roots are then displaced radially off the unit circle to achieve null-filling. The result is a shaped beam with low, equal-percentage ripple, and sidelobe heights in the nonshaped region that are individually controlled. The procedure is illustrated for a linear array, designed to produce a \csc ^{2}\theta \cos\theta pattern. View full abstract»

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  • Penetrating electromagnetic wave applicators

    Publication Year: 1984 , Page(s): 1138 - 1141
    Cited by:  Papers (6)
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    It is demonstrated that in the near field of suitably designed applicators, the penetration depth of the electromagnetic wave can greatly exceed the usual skin depth. The application of this principle in therapy is suggested. View full abstract»

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  • Optimum location of the wobble axis of secondary mirrors in cassegrain-type telescopes

    Publication Year: 1984 , Page(s): 1128 - 1129
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    The best position for the rotation axis of the wobbling secondary mirror in a Cassegrain type of antenna is through the focal point of the main mirror: the prime focus. Compared to the usual situation, where the axis of rotation contains the vertex of the secondary mirror, this means a considerable improvement of beam quality, especially at large wobble angles. View full abstract»

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  • Power focusing characteristics of ellipsoidal reflector

    Publication Year: 1984 , Page(s): 1033 - 1039
    Cited by:  Papers (2)
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    Power focusing characteristics of a prolate spheroidal reflector, the aperture of which is parallel to the line connecting the two focuses, are numerically studied. As a transmitting and a receiving antenna, linear wires with finite length are placed at or near the focuses of the reflector. Reflected near fields from the reflector are calculated by the physical optics technique, and transmitting and receiving antenna characteristics are obtained by the method of moments. Calculated results are given for the power focusing characteristics as a function of the eccentricity, the aperture size of the reflector, antenna directions, antenna lengths, and the receiving antenna displacement. Better power focusing characteristics are obtained when the transmitting antenna becomes less directive, or the size of the aperture becomes larger. Measured and calculated results agree very well. View full abstract»

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  • Limitations and defects of certain inverse scattering theories

    Publication Year: 1984 , Page(s): 1080 - 1088
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    Recently some new formulations for the inverse scattering problem were developed resulting in the "exact inverse scattering theory," which promises to be a more general background for different other methods. This theory consists essentially of the construction of "effectal fields" inside a closed surface, on which the monochromatic scattered field and its normal derivative are known. Outgoing from the "effectal fields" several methods were proposed to reconstruct the scattered field, its equivalent sources or just to visualize the scattering geometry. Recent discussions on this subject have issued controversy concerning the exactness, uniqueness, and applicability of these methods. Applying them to synthetic examples and practical problems we are able to confirm the results of Devaney et al. with emphasis on the following facts: in two versions, the "exact inverse scattering theory" is incorrect, and, in another one, it does not yield a better solution than generalized holography. Only broad-band excitation or multiple experiments yield further information about the scatterer, but then, approximations concerning the sources and scatterers have to be introduced. 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