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Antennas and Propagation, IEEE Transactions on

Issue 4 • Date July 1969

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Displaying Results 1 - 20 of 20
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Preface

    Page(s): 406
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    Freely Available from IEEE
  • [Back cover]

    Page(s): c4
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    Freely Available from IEEE
  • An omnidirectional microwave antenna for use on spacecraft

    Page(s): 459 - 466
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    The qualitative theory, design, and development of a parallel-plate waveguide-fed antenna, suitable for flush-mounted broad-band spacecraft applications, are presented. The antenna makes use of wedge-like metal posts placed uniformly about the periphery of the feed plates to provide both structural strength and practical interconnection routes for cables without disrupting the antenna impedance and patterns. Measurements taken on the antenna, which is mounted on spheroids up to 50 wavelengths in circumference, are presented; equatorial patterns are omnidirectional withinpm 0.25dB, and polar patterns have beam widths similar to a half-wave dipole. View full abstract»

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  • Radiation characteristics of a cavity-backed cylindrical gap antenna

    Page(s): 467 - 477
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    The input impedance and the equatorial radiation patterns of a VHF cavity-backed cylindrical gap antenna are derived and compared with experiments. The experiments generally support the computations, provided that the gap dimension is neither larger than about 1/100 of a wavelength, nor so thin that mechanical tolerances in the feed design become important. The results show that the tuning, impedance bandwidth, and the radiation patterns of this antenna can be controlled very accurately by adjusting the internal radius and height of the cavity. Salient points of this antenna are its wide-band characteristics (10-percent bandwidth), its pattern circularity, and particularly the fact that it can be made an integral part of a space vehicle. View full abstract»

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  • ATS mechanically despun communications satellite antenna

    Page(s): 415 - 428
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    The antenna system described is one of the experiments on NASAs ATS-III spin stabilized satellite that was launched on November 5, 1967. It was put into synchronous orbit shortly thereafter and has been operating satisfactorily since. Using a line source feed illuminating a parabolic cylindrical reflector, a linearly polarized gain over 17 dB is achieved. The antenna is positioned by means of a vernier type stepping motor-drive system that points the antenna beam towards earth within approximatelypm0.7degree in accordance with instructions received on the satellite from the ground control station. Prior to launch, the antenna system was subjected to extensive qualification testing. Confidence in a desired five-year life in orbit for the motor-drive system was obtained by testing the lubrication system and bearings for 7800 hours at temperatures ranging from-80degF to+120degF at vacuum pressures as low as1 times 10^{-8}torr. View full abstract»

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  • Multifunction single-package antenna system for spin-stabilized near-synchronous satellite

    Page(s): 435 - 442
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    An antenna system is described for a spin-stabilized satellite with its axis normal to the orbital plane. Three antennas in a compact lightweight package comprise the antenna system: a switched-beamX-band transmitting antenna, an omnidirectionalX-band receiving antenna and an omnidirectional VHF telemetry antenna. The first is a cluster of eight circularly polarized horns pointed radially outward every 45 degrees about the spin axis. An eight-throw solid-state waveguide switch turns on that horn currently pointing most nearly to earth. This is accomplished by providing the switch with electrical signals from a logic circuit operating on information from earth sensors. The second antenna is a circularly polarized biconical horn located above the cluster of transmitting horns. Its sense of polarization is opposite that of the transmitting antenna, and a filter in the transmission line to the receiver insures the required isolation. The third antenna is obtained by feeding across the gap between the twoX-band antennas and exciting the external surfaces to radiate in a linearly polarized mode. Total weight of the three-antenna package is less than4frac{1}{2}pounds; it occupies a volume less than 10 inches square by 8 inches high above the top panel of the satellite. View full abstract»

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  • Prolate spheroidal antennas in isotropic plasma media

    Page(s): 496 - 506
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    The problems of a gap-excited finite-sized prolate spheroidal antenna, with and without a confocal prolate spheroidal vacuum sheath, operated in a uniform cold and in a uniform warm lossy plasma medium, have been considered by applying boundary value problem techniques. The dependence of the input admittance, the current distribution, and the radiation pattern, upon the collision frequency, the electron temperature, the length of the antenna, the length-to-radius ratio for the antenna, the ratio of the plasma frequency to the operating frequency, and the thickness of a vacuum sheath have been investigated. Admittance curves are given from which the input admittance of a finite linear antenna can be estimated for a wide range of operating conditions and length-to-radius ratios. Conductance and susceptance maxima, dependent upon the vacuum sheath thickness, have been observed when using the cold plasma model foromega < omega_{p}. When using the warm plasma model in conjunction with the boundary condition that the normal component of the fluid velocity is zero at the antenna surface and at the vacuum sheath surface, the radiation resistance of the antenna is increased significantly for the parameters considered. View full abstract»

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  • Monopole and conic antennas on spherical vehicles

    Page(s): 477 - 484
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    The radiation and impedance characteristics of a spherically capped conic antenna protruding from a spherical vehicle are studied as a function of cone height, cone angle, and diameter of the vehicle. The conic antenna is excited by a gap at the cone base. The excitation is assumed rotationally symmetric. Considered in detail is the thin conical monopole extending from a sphere. The radiation patterns and antenna impedance referred to the base are calculated and compared with that of a cylindrical monopole over an infinite conducting plane. View full abstract»

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  • Spacecraft phased array configurations

    Page(s): 522 - 524
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    Ideas of spacecratt phased array configurations are described in this communication. The aperture of the phased array is 28.5 by 28.5 feet. View full abstract»

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  • Pattern synthesis of circular arrays in a moving medium

    Page(s): 524 - 526
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    Based on a modified expression for the radiation field of a circular array in a moving medium, pattern synthesis is performed for medium motion both in the direction of and parallel to the main beam. It is shown that medium motion, even considering only first-order effects, changes the synthesized patterns significantly. The required excitation amplitudes and phases for the proper synthesis of a 21-element circular array to yield a cosine-square pattern in a moving medium are given. View full abstract»

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  • A deployable cross LPD array on a conducting cone

    Page(s): 428 - 435
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    A deployable cross log periodic dipole (LPD) array on a conducting cone has been designed and tested at M.I.T. Lincoln Laboratory as part of the RSP (Reentry Systems Program) flight program. This paper presents a brief mechanical description and an electrical performance of this LPD array. The electrical property of the antenna was fouud to be quite good within the frequency band designed. The ground test has indicated that the structure is able to deploy under a Nike-Hydac launch environment. The antenna has demonstrated a potential application to a space or missile body which may require a frequency-independent antenna in VHF-UHF band. View full abstract»

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  • Radiation from a circularly polarized antenna through the ionized wake of a Mars-entry capsule

    Page(s): 488 - 495
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    The effects of the ionized wake-of a Mars-entry capsule on radiation from a circularly polarized antenna operating at 400 and 2295 MHz are studied. The circularly polarized antenna is represented by a turnstile antennalambda/4above a ground plane, while the ionized wake is approximated by a cylindrically stratified plasma consisting ofN-plasma regions. Integral expressions for the fields are obtained for the antenna located in the wake and are evaluated using saddle-point integration to yield the radiation patterns. Computed patterns for the two simplest configurationsN = 1andN = 2are presented. The radiation patterns for both near- and far-wake electron-density profiles develop a conical null region whose extent is proportional to the peak electron density in the wake. For the near-wake electron-density profile, sharp peaks which are attributable to leaky-wave radiation, appear within the null region of the patterns. The effect of the conical null region in the patterns is to prolong blackout time for communication cone angles that lie within the null region. There are no serious depolarization effects in the nonnull region and satisfactory communications can be carried out. View full abstract»

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  • VHF antenna systems for spin-stabilized satellites

    Page(s): 443 - 451
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    Lincoln Laboratory has developed two circularly polarized VHF antenna systems for use on spin-stabilized satellites, Both are described, and test results are discussed. One is a low-gain (3-dB) antenna with omnidirectional coverage in the equatorial plane. The second is a high-gain (10-dB) antenna with a despun beam electronically scanned to always be Earth directed. Development of the component dipole and slot array elements is explained, and performance data are given for the final flight configuration. View full abstract»

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  • A probabilistic approach to large circular and spherical arrays

    Page(s): 514 - 522
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    Antenna arrays with elements distributed at random in a three-dimensional space are studied. Arbitrary excitation and nonisotropic elements are considered. The distribution of the sidelobe level below a certain value for all directions of observation, as well as other probabilistic properties are determined approximately. These general results are then applied to circular and spherical arrays. In particular, for the latter case, conical log-spiral antennas are considered in some detail. It is found that for large arrays with high resolution, the required number of elements can be several orders of magnitude smaller than what is commonly required on the basis of one element per(lambda/2)^{2}Finally, a few experiments simulated by the Monte Carlo method were conducted and excellent agreements with theory have been found in all cases. View full abstract»

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  • Performance analysis of planar hybrid matrix arrays

    Page(s): 526 - 528
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    An analysis is presented of overall aperture efficiency, weight, and control power requirements for hybrid matrix arrays in synchronous satellite applications. An array is described which is mounted on a 7-foot aperture in a triangular grid fashion and fed by a hybrid matrix consisting of 3-port building blocks which in turn are fed by 9-port matrices. The beam crossover loss is minimized by beam combining at the outputs of the 9 ports. Component losses are analyzed, and residual array gains are calculated for the 7-foot aperture as a function of operating frequency. It is concluded that arrays of this type are practical for net gains of up to 30 dB. View full abstract»

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  • The design of the mechanically despun antenna for the Intelsat III communications satellite

    Page(s): 407 - 415
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    The use of a spin-stabilized communications satellite of large channel capacity requires a high-gain antenna which may be despun, mechanically or electronically, with respect to the satellite. The design of a mechanically despun antenna system for the Intelsat-III communications satellite is discussed. The communications signals utilize a high-gain directive antenna which is mechanically despun while an omnidirectional antenna is used for the telemetry information. Positional control of the directional antenna is provided by the control electronics subsystem such that the antenna is always pointed directly at the earth. Satellite-borne infrared earth sensors provide earth reference pulses to the control electronic subsystem for antenna despin stabilization and pointing. Also discussed is the bearing and lubrication system for the antenna drive assembly. In-orbit performance of the two systems launched is also given. View full abstract»

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  • Relativistic communications effects associated with moving space antennas

    Page(s): 484 - 488
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    Future space missions may require vehicles traveling at relativistic velocities. Consequently, relativistic effects will have to be considered in the development of future space communication systems. This paper presents a formulation of these relativistic communication effects which are not normally encountered by the designer. The gain function, power density available at the receiver and apparent frequency of the source can be greatly affected by the motion of the space craft antenna. In addition, the apparent direction of the space craft can be quite different from its actual direction for both the transmitting and receiving conditions. Formulations are presented by which these effects are described for an arbitrary antenna in terms of the antenna characteristics in its rest frame and the actual space craft location, a form that is convenient for the designer. In addition, numerical examples are shown to illustrate the magnitude of these relativistic effects. View full abstract»

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  • Aperture radiation from an axially slotted elliptical conducting cylinder using geometrical theory of diffraction

    Page(s): 507 - 513
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    The equatorial radiation pattern of a parallel-plate TEM mode axial slot on an infinite cylinder of elliptical cross section is computed using wedge-diffraction and creeping-wave theory. The wedge-diffracted fields are obtained by the diffraction interaction from a set of infinite wedges approximating the parallel-plate-cylinder geometry. Surface-wave propagation on curved bodies commonly used in scattering is employed for the creeping-wave contribution. The total field in the lit region is approximated using superposition of wedge-diffracted and creeping-wave fields and in the shadow region solely by creeping-wave fields. The computed patterns are compared with experimental results since boundary-value solutions are not readily available. Good agreement between theory and experiment is indicated. View full abstract»

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  • Large-aperture expandable truss microwave antenna

    Page(s): 452 - 458
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    A space erectable truss antenna concept capable of deploying a rigid, lightweight (0.1 lb/ft2of aperture), parabolic reflector from 5 to 300 feet in diameter is discussed. A three-dimensional spring-loaded truss retracts into three optional packaging configurations, such that, a 100-foot diameter antenna can be packaged into a 10-foot payload envelope. Depth of the deployed antenna truss reduces thermal distortion enabling surface tolerance-to-diameter ratios less than2 times 10^{-4}to be achieved over the orbit. While the deployment is completely automatic, all functions can be supported by an astronaut. RF tests have been conducted on a 6-foot working model at 15 GHz with a peak gain frequency projected at 30 GHz. View full abstract»

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Aims & Scope

IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Meet Our Editors

Editor-in-Chief                                                 Kwok W. Leung