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Antennas and Propagation, IRE Transactions on

Issue 2 • Date March 1961

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Displaying Results 1 - 25 of 28
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • A triangular arrangement of planar-array elements that reduces the number needed

    Page(s): 126 - 129
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    In this paper, it is shown that by arranging the elements of a beam-scanning planar antenna array in a triangular pattern rather than a rectangular pattern, the number of elements needed in the array is reduced. (The number of elements needed in an array is determined from the requirement that no spurious beams form in the array pattern.) The reduction in the number of elements depends upon the solid angle over which the main beam is positioned. If the main beam is positioned within a constant angle about the array normal, then the number of elements can be reduced by 13.4 per cent by arranging the elements in a pattern of equilateral triangles rather than in a square pattern. If the main beam is positioned within a "pyramid," centered about the array normal, then the reduction is usually less than 13.4 per cent. Graphs are included showing for both element arrangements the solid angle over which the main beam can be scanned without the formation of spurious beams. View full abstract»

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  • A study of the coma-corrected zoned mirror by diffraction theory

    Page(s): 130 - 139
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    A two dimensional coma-corrected zoned mirror has been investigated by a rigorous integral equation formulation, for whose solution a procedure of successive approximation can be established. For computational convenience, the exact first order solution is again approximated. The error committed in this approximation is investigated. The higher order solutions due to couplings between zones are not significant so far as the image field is concerned. In the example studied, it is found that for a system with smallF-number and an illumination of small taper the coma aberration of this zoned mirror is practically eliminated for scan angles up to25deg, in sharp contrast to a smooth parabola whose scanning characteristics are also presented for comparison. However, the chromatic aberration overshadows this advantage for a wide-band application; the total bandwidth of this example is only a few per cent. View full abstract»

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  • Microwave antennas derived from the cassegrain telescope

    Page(s): 140 - 153
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    A microwave antenna can be designed in the form of two reflecting dishes and a feed, based on the principle of the Cassegrain optical telescope. There are a variety of shapes and sizes available, all described by the same set of equations. The essential performance of a Cassegrain double-reflector system may be easily analyzed by means of the equivalent-parabola single-reflector concept. Techniques are available for reducing the aperture blocking by the sub dish of the Cassegraln system: one method minimizes the blocking by optimizing the geometry of the feed and sub dish; other methods avoid the blocking by means of polarization-twisting schemes. The former method yields good performance in a simple Cassegrain antenna when the beamwidth is about1degor less. The latter methods are available for any application not requiring polarization diversity, and an optimized set of polarization-operative surfaces has been developed for these twisting Cassegrain antennas. Experimental results, presented for practical antennas of both types, illustrate the feasibility of these principles. A number of unusual benefits have been obtained in the various Cassegrain antenna designs, and additional interesting features remain to be exploited. View full abstract»

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  • Multiple beams from linear arrays

    Page(s): 154 - 161
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    The problem of devising a passive RF transmission line feed system to provide independent multiple outputs from a linear array is considered. It is shown that a lossless, matched feed network is possible only for uniform aperture distribution. The general feed system for connecting2^{n}inputs to2^{n}elements is shown to consist of conventional hybrid junctions with associated phase shifters. In order to increase the possible number of elements in the array, the problem of finding applicable junctions more complex than the hybrid is considered. Junctions with three inputs and three outputs and with four inputs and four outputs are derived for use in multiple feed networks, expanding the number of elements in the array to2^{l}3^{m}4^{n}. View full abstract»

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  • A new technique for electronic scanning

    Page(s): 162 - 166
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    The concept of time-modulated antennas has recently been demonstrated as a means of overcoming many of the limitations currently restricting advances in the antenna art. Of special importance is the mathematical possibility of generating a pattern complex capable of providing simultaneous scan operation. This characteristic is realized by periodic time modulation of the aperture distribution. This paper discusses the theory of simultaneous "scanning" using time modulation techniques and shows that the required pattern complex is generated by a progressive-pulse aperture excitation. The fundamental equations and relationships concerning the form of pulse excitation and "scanning" coverage are derived. In addition, practical methods of physically generating the proper pulse-excited aperture are described, and the necessary detection requirements are delineated. View full abstract»

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  • Cylindrical shields

    Page(s): 166 - 170
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    The effectiveness of an imperfectly-conducting cylindrical shield of small cross section depends on both the attenuation through the metal wall of the externally maintained field and the amplitude of the current that is induced in the cylinder. When the length of the cylinder, which behaves like a linear scattering antenna, approaches a resonant value, the currents induced in the walls and the field inside the tube are relatively large. Under these conditions, large currents may be induced in a thin dipole placed coaxially within the shield. View full abstract»

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  • Folded dipoles and loops

    Page(s): 171 - 187
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    In Section I the theory of linear arrays consisting of two or more closely spaced elements that are interconnected by lumped reactances is reviewed. Specific application is made to two-element end-loaded folded dipoles and monopoles constructed of conductors with different diameters, to series tuned three-wire folded dipoles and monopoles, and to a three-wire-line reactor and impedance transformer. In Section II the circular folded dipole or Halo antenna is treated. View full abstract»

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  • Sidelobe reduction by nonuniform element spacing

    Page(s): 187 - 192
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    A perturbational procedure for reducing the sidelobe level of discrete linear arrays with uniform amplitude excitation by using nonuniform element spacing is presented. The calculation of the required element spacings is quite simple. The method can reduce the sidelobe level to about2/Ntimes the field intensity of the main lobe, whereNis the total number of elements, without increasing the beamwidth of the main lobe. Several examples are given. View full abstract»

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  • Photoconductive modulation of microwave electric fields

    Page(s): 193 - 199
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    Thin films and coatings of photoconductive cadmium sulfide material are being used to modulate electric fields. This paper analyzes these films in terms of the physics involved and the effect upon microwave fields. Experimental procedures show the validity of the analyses and indicate possible applications of the principle. Practical significance of the technique is illustrated by experimentally determining the areas of a particular flat plate that produce the first sidelobe of the scattering pattern. View full abstract»

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  • Diffraction of a plane wave by an infinite slit in a unidirectionally conducting screen

    Page(s): 199 - 207
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    The scattering of a plane electromagnetic wave of wave numberk, by an infinite slit (of width2a) formed by two unidirectionally conducting, semi-infinite coplanar screens of zero thickness is considered. By employing an integral equation procedure, a rigorous asymptotic solution is obtained up to order(ka)^{-5/2}. The currents induced on the screens and the first few terms in the transmission coefficient are evaluated. The similarity between this and the corresponding problem involving perfectly conducting screens is pointed out. View full abstract»

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  • Refraction compensation in a spherically stratified ionosphere

    Page(s): 207 - 210
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    For satellite orbit determinations, it is necessary to know the range to the satellite with great accuracy. The presence of the ionosphere with a frequency-dependent index of refraction produces errors in range measurements made by either CW (Doppler) or pulse radio techniques. A measurement scheme is proposed that gives the instantaneously-corrected range for a spherically stratified ionosphere without recourse to any further assumptions about the electron density profile. The corrected range is given by the average of the CW and pulse range measurements and is free of the first-order error contributed by the inverse frequency-squared term in the refractive index. This scheme is shown to be slightly more effective than a scheme combining the results of two CW range measurements. Expressions are also derived for the higher-order residual errors which remain after the proposed compensation, and the expressions for the variation in arrival angle with frequency are given. These expressions depend upon the integrated effect of the free electrons; consequently, a calculation with a simple profile should yield typical results. The compensated range error and the residual errors are given for a satellite at a height of 640 km, arrival angles in the first quadrant, and at a frequency of 100 Mc. This compensation scheme cancels all but a few per cent of the original range error. View full abstract»

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  • Scatter communications with radar chaff

    Page(s): 211 - 217
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    The first part of this paper is concerned with finding an analytical expression for the scattering cross section of chaff oriented randomly within a vertical cone. The dipoles are allowed to take on all the angles within this cone. A vertically-polarized receiver is assumed off on the horizon and the transmitter on the ground below the chaff. The cross section is a function of the conical angle of the configuration and the angle between a normal to the ground and the incident electric field from the transmitter. Fig. 2 is a plot of the scattering cross section as a function of these two angles. Half-wave chaff randomly distributed within a conical angle about a vertical is not the most effective ensemble, but is a practical one at the lower frequencies. Cutting all these half-wave dipoles into very short ones makes it practical to place them in a horizontal position which has an ensemble gain over the conical but a reradiation loss, since short dipoles are less effective scatters than half-wave ones. The second part of this paper compares the reradiation loss and horizontal ensemble gain. View full abstract»

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  • Diffraction by a slit

    Page(s): 217 - 219
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    The electric field diffracted by a strip caused by an incident cylindrical wave with E parallel to the edge, at various angles of incidence, is measured in a parallel plane medium. The field is compared with that computed from geometrical optics currents and with the addition of equivalent line currents at the edges. The edge "line currents" improve the geometrical optics current field particularly at oblique incidence. View full abstract»

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  • Multiple-parameter presentation of radar meteor echoes

    Page(s): 221
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    A circuit is given enabling the range, time of occurrence, duration, maximum amplitude, and amplitude variations in radar echoes from meteor trails to be presented on a single-beam oscillograph. View full abstract»

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  • Octave-bandwith feed horn for paraboloid

    Page(s): 223 - 224
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    First Page of the Article
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Aims & Scope

The Transactions ceased publication in 1962. The current retitled publication is IEEE Transactions on Antennas and Propagation.

Full Aims & Scope