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Antennas and Propagation, IEEE Transactions on

Issue 3 • Date May 1979

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Displaying Results 1 - 25 of 29
  • [Front cover and table of contents]

    Publication Year: 1979 , Page(s): 0
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    Freely Available from IEEE
  • Comments on "Mutual coupling between two waveguide radiators on a conducting concave sectoral surface"

    Publication Year: 1979 , Page(s): 444
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    First Page of the Article
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  • Characterization of the random array peak sidelobe

    Publication Year: 1979 , Page(s): 379 - 385
    Cited by:  Papers (11)
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    Upper bounds on the height of the peak sidelobe of the random array are derived using the theory of level crossings of a random process. Statistical properties of the random array beam pattern are presented and are used to calculate the expected number of up-crossings of a given level by the power pattern. Upper bounds on the peak sidelobe height are obtained using the expected number of up-crossings. The bounds are compared with computer simulation results. View full abstract»

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  • An experimental study of electronic scanning by an antenna loaded with a circular array of ferrite rods

    Publication Year: 1979 , Page(s): 426 - 429
    Cited by:  Papers (13)
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    The measured performances of the antenna which consists of a circular array of 12 anisotropic ferrite rods, a truncated biconical horn, and a core wire of a coaxial cable at the center of the biconical horn are presented. The following are made clear. The transmitting pattern having a single big lobe and suppressed sidelobes is obtained by the effects of the appropriate ferrite anisotropy and of the interactions among the ferrite rods. The main lobe cannot be rotated continuously, but at intervals of about 30\deg by gradually changing the axial magnetic fields applied to the respective ferrites; that agrees with what was expected by the two-dimensional theory. Reciprocity does not hold for this antenna: the receiving pattern coincides with the transmitting pattern rotated 180\deg . Hence, this antenna permits us to receive from a direction and simultaneously to transmit in a different direction. The frequency characteristics of the antenna including the input impedance are also shown and discussed. View full abstract»

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  • Plane-wave expansion for arrays of arbitrarily oriented piecewise linear elements and its application in determining the impedance of a single linear antenna in a lossy half-space

    Publication Year: 1979 , Page(s): 331 - 343
    Cited by:  Papers (80)
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    An infinite array of arbitrarily oriented identical elements with arbitrary identical currents is considered. The field from this array is expanded into plane inhomogeneous waves, and the mutual impedance between the array elements and an exterior arbitrarily oriented element is derived. The formulation is particularly useful when the array is located adjacent to a dielectric interface. Numerical examples are given and the relationship to earlier formulations pointed out. It is further shown that the impedance of a single element can be obtained as the average of the scan impedance taken over the entire hemisphere (called the array scanning method (ASM)). This technique has a clear physical interpretation which greatly facilitates its uses, which include the moment method solutions of wire antennas as applied to the Sommerfeld integral. Numerical evaluation is straightforward when the dipole is in the lossy half-space, and the utility of the method is demonstrated by the presentation of results for the input impedance of dipoles in a variety of half-space environments. Solution is by Galerkin's method with a piecewise sinusoidal expansion for the current. Computer time is proportional to d^{-1} , where d is the distance of the dipole to the interface. For conducting media and low frequencies an approximation is made to reduce computation time. The moment method solution of a dipole buried at a depth as small as 1/150000 wavelength in the earth is presented. View full abstract»

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  • On pulse compression in dispersive media

    Publication Year: 1979 , Page(s): 420 - 422
    Cited by:  Papers (2)
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    A comparison between three methods used for the synthesis of suitable signals which result in pulse compression, when transmitted through dispersive media, is presented. These are the equalization of group-time delay method, the space-time rays method, and the matched-signal method. The three methods are shown to be equivalent if the signals are restricted to be frequency-modulated with uniform envelopes. A generalized expression for the requited frequency modulation law for pulse compression in an inhomogeneous dispersive medium is obtained. Considerations for lossy dispersive media and additional optimization of the signal envelope are also discussed. View full abstract»

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  • Predictive methods for rain attenuation using radar and in-situ measurements tested against the 28-GHz Comstar beacon signal

    Publication Year: 1979 , Page(s): 398 - 406
    Cited by:  Papers (10)
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    A program to measure the rain attenuation of the Comstar beacon signal at 28.56 GHz has been in continuous operation since March of 1977 at Wallops Island, VA. During the summer of 1977 simultaneous radar and disdrometer measurements at the site were also made and used for predicting path attenuation. The best-fit values of a and b of the relation k = aZ^{b} were deduced for each rain period from the raindrop size measurements, where k is the attenuation coefficient [dB/km] and Z is the reflectivity factor [mm6/m3]. The measured k-Z relations and the simultaneous radar reflectivity measurements along the beacon path were injected into a computer program for estimating the path attenuation. Predicted attenuations, when compared with the directly measured ones, show generally good correlation on a case-by-case basis and very good agreement statistically after an empirical calibration adjustment is applied to the radar data. A method was also tested for predicting fade statistics at another frequency (e.g., 19 GHz) using simultaneous rain rate and fade distributions (28 GHz) in conjunction with disdrometer data. The predicted distributions showed good agreement with radar-predicted levels. The results demonstrate the utility of using radar in conjunction with disdrometer and rain gauge measurements for predicting fade events, long-term fade distributions, and establishing predictive criteria associated with earth-satellite telecommunications. View full abstract»

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  • Calculated scan characteristics of a large spherical reflector antenna

    Publication Year: 1979 , Page(s): 430 - 431
    Cited by:  Papers (3)
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    A previously published numerical method to calculate the radiation properties of parabolic reflectors has been modified to also include very large spherical reflectors. The method has been verified by comparing the calculated and the measured results for a 120-wavelength spherical reflector. View full abstract»

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  • Diffraction by an arbitrary subreflector: GTD solution

    Publication Year: 1979 , Page(s): 305 - 316
    Cited by:  Papers (2)
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    The high-frequency asymptotic solution of diffraction by a conducting subreflector is studied. By using Keller's geometrical theory of diffraction and the newly developed uniform asymptotic theory of diffraction, the scattered field is determined up to an including terms of order k^{-1/2} relative to the incident field. The key feature of the present work is that the surface of the subreflector is completely arbitrary. In fact, it is only necessary to specify the surface at a set of discrete points over a random net. Our computer program will fit those points by cubic spline functions and calculate the necessary geometrical parameters of the subreflector. In a companion paper by Y. Rahmat-Samii, R. Mittra, and V. Galindo-Israel, the scattered field from the submflector is used to calculate the secondary pattern of an arbitrarily shaped reflector by a series expansion method. Thus, in these two papers, it is hoped that we have developed a "universal" computer program that can analyze most dual-reflector antennas currently conceivable. It should also be added that our method of calculation is extremely numerically efficient. In many cases, it is one order of magnitude faster than the conventional integration method based on physical optics. View full abstract»

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  • Scattering of obliquely incident plane waves from a finite periodic structure of ferrite cylinders

    Publication Year: 1979 , Page(s): 317 - 323
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    For the scattering of waves obliquely incident on many homogeneous gyrotropic cylinders simultaneous matrix equations are first derived from the reciprocity theorem where the auxiliary electric and magnetic current sources are specially selected. As a numerical example we examine the scattering properties of a finite periodic structure composed of many circular ferrite cylinders, with attention to 1) the frequency characteristics of the scattering cross section where the parameters are the number of cylinders, the incident angle, and the applied static magnetic field; 2) the patterns of the scattered power density; 3) the distributions of the total field in the vicinity of the cylinders; 4) the role of the periodicity of the spacing of the scatterers on the scattering cross section; and 5) the effect of the interactions among the cylinders. The extension of the present method may make it possible to analyse guided modes along an array of gyrotropic cylinders. View full abstract»

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  • Reflector aperture-blocking by a loaded wire feed

    Publication Year: 1979 , Page(s): 422 - 425
    Cited by:  Papers (2)
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    A technique for computing the total aperture-blockage effect of a loaded wire antenna feeding a paraboloidal reflector is described. First an analytical formulation for determining the fields scattered by a field incident upon a loaded wire antenna is described, and then an iterative procedure utilizing this result to obtain the aperture blockage effect is given. Typical results are presented for both simple and complex feed structures. View full abstract»

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  • The influence of aperture shape on the radiation patterns of horn-reflector antennas

    Publication Year: 1979 , Page(s): 435 - 438
    Cited by:  Papers (1)
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    The role of aperture shape in influencing the far-zone radiation pattern in the vicinity of the main beam of horn-reflector antennas is examined. The three major types of horn-reflector antennas are considered-pyramidal, diagonal, and conical-and the influence of their aperture shape on the spatial character of antenna radiation is assessed. View full abstract»

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  • The design of linearly polarized slotted waveguide feeds for spherical reflectors

    Publication Year: 1979 , Page(s): 289 - 293
    Cited by:  Papers (1)
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    A procedure for the design of linearly polarized slotted waveguide line feeds for spherical reflector antennas is described. The necessary equations for determining the complex propagation constant \alpha + j\beta in a line source are given in terms of reflector parameters. Guide and slot dimensions that will yield the desired \alpha and \beta are then found by making use of experimental data, presented herein. These data consist of measured values of \alpha and \beta as functions of slot length for a number of slotted waveguide test sections of various widths. The technique is applicable over a wide range of frequencies and reflector sizes. An example is given in which a feed is designed at 1420 MHz to illuminate 700 ft of aperture in the Arecibo spherical reflector. View full abstract»

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  • Mode matching analysis of biplanar slot arrays

    Publication Year: 1979 , Page(s): 441 - 443
    Cited by:  Papers (13)  |  Patents (1)
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    A modal matching analysis of biplanar slot arrays imbedded in dielectric layers is presented. Calculated and measured results show that, with proper design, the dielectric matching layers can be adjusted to produce a biplanar slot array with a wide low-loss passband. Further, the bandwidth will be much less dependent on the incidence angle than in similar arrays without dielectric matching layers. One interesting feature of the investigation was the appearance of an unexpected passband null due to the dielectric filler material which occurs at a lower frequency than any possible Wood's anomaly. This null was first predicted theoretically and later confirmed by measurements. By modifying the spacing between the slots this null can be removed from the passband. View full abstract»

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  • Wave tilt sounding of a linearly inhomogeneous layered half-space

    Publication Year: 1979 , Page(s): 417 - 419
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    The wave tilt of a transverse electric (TE) electromagnetic wave over a linearly inhomogeneous lossy layer overlying a homogeneous half-space is studied. Two approaches are used: an exact formulation using solutions of Airy's equation and an approximate numerical solution using a large number of homogeneous layers with a linearly increasing dielectric constant. The numerical results of both solutions are practically identical as long as the thickness of the layers in the approximate model are somewhat smaller than a quarter-wavelength. View full abstract»

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  • Interaction of electromagnetic and acoustic waves in a stochastic atmosphere

    Publication Year: 1979 , Page(s): 385 - 393
    Cited by:  Papers (7)
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    In the Stanford radio acoustic sounding system (RASS) an electromagnetic signal is made to scatter from a moving acoustic pulse train. Under a Bragg-scatter condition maximum electromagnetic scattering occurs. The scattered radio signal contains temperature and wind information as a function of the acoustic-pulse position. In this investigation RASS performance is assessed in an atmosphere characterized by the presence of turbulence and mean atmospheric parameters. The only assumption made is that the electromagnetic wave is not affected by stochastic perturbations in the atmosphere. It is concluded that the received radio signal depends strongly on the intensity of turbulence for altitudes of the acoustic pulse greater than the coherence length of propagation. The effect of mean vertical wind and mean temperature on the strength of the received signal is also demonstrated to be insignificant. Mean horizontal winds, however, shift the focus of the reflected electromagnetic energy from its origin, resulting in a decrease in received signal level when a monostatic radio-frequency (RF) system is used. For a bistatic radar configuration with space-diversified receiving antennas, the shifting of the acoustic pulse makes possible the remote measurement of the horizontal wind component. View full abstract»

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  • Optimization of radio tracking frequencies

    Publication Year: 1979 , Page(s): 393 - 397
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    The three major factors which limit the performance of animal radio tracking systems: propagation loss, antenna detuning, and signal variability are described. Propagation loss for antenna heights from ground level to 2 m at five frequencies between 70 and 1250 MHz has been measured in mangroves and shows high loss at high frequency. However, an analysis of the environmental sensitivity of small antennas shows that high detuning losses are easily obtained at low frequency; these two factors combine to give a broad optimum frequency range between 500-1000 MHz. Using a simple scattering model it is shown that signal variability, caused by scattering from surrounding vegetation, rises rapidly with frequency. As a result the lowest practical frequency is recommended; in the case of the animal tracking system modeled here, frequencies of 500-800 MHz appear best. View full abstract»

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  • Scattering from periodic arrays of crossed dipoles

    Publication Year: 1979 , Page(s): 323 - 330
    Cited by:  Papers (24)  |  Patents (1)
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    An analysis is presented for calculating the scattering from periodic arrays of symmetrical crossed dipoles. It is shown that in general the reflection coefficient versus frequency of symmetrical crossed-dipole arrays exhibits two distinct resonances, which occur when the dipole elements are on the order of a half-wavelength long. The analysis reveals also the presence of an antiresonance, which occurs at a frequency between the two resonances. At the antiresonant frequency the array reflection coefficient is zero. Thus, within a relatively narrow frequency band, the array reflection characteristics traverse the extremes of complete reflection followed by no reflection, and finally by complete reflection again. The anomalous reflection versus frequency behavior in such arrays is shown to be directly attributable to two distinct resonances excited in the crossed elements. For an isolated crossed dipole, it is shown that the total induced current can be approximately represented by two uncoupled current components. The current components induced on the same elements in an array, however, are coupled to one another through interaction with neighboring elements. The coupling results in complete cancellation of the total bistatic array scattering, at a frequency which lies between the two component current resonant frequencies. View full abstract»

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  • On reflected rays in axisymmetric radomes

    Publication Year: 1979 , Page(s): 432 - 435
    Cited by:  Papers (5)
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    A method is derived by which rays that reflect off the interior of a radome in a specific direction are found. It is demonstrated that these rays (if they exist) depend upon the gimbal angle. It is observed that they do not exist for gimbal angles less than a "critical gimbal angle." It is demonstrated that the critical gimbal angle is a function of the fineness ratio of the radome. Results are given for several radome geometries. View full abstract»

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  • GTD analysis of the radiation patterns of open-ended circular cylindrical waveguide horns

    Publication Year: 1979 , Page(s): 438 - 441
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    GTD analysis of the principal plane radiation patterns of open-ended circular cylindrical waveguide horns excited in the TE_{11} mode is presented, based on the theory of Kouyoumjian et al. [5]- [7] and the slope diffraction formulation [2]. The study enables one to predict accurately the E - and H -plane patterns over the neat and far sidelobes and backlobes of the horn, and a good agreement is noticed between the calculated and measured radiation patterns obtained with an experimental circular waveguide horn excited in the dominant mode. View full abstract»

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  • Summary of results of a recent sea clutter measurement program

    Publication Year: 1979 , Page(s): 416 - 417
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    Measurements of the distribution of reflectivity ( \sigma _{0} ) are presented for the sea at X band. View full abstract»

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  • Position-modulated phased array-space factor considerations

    Publication Year: 1979 , Page(s): 373 - 378
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    The space factor of an element position-modulated array is expressed as an Anger function series for a general amplitude distribution. The behavior of the main lobe and the diffraction sidelobes for uniform excitation are presented in the form of universal curves. It is found that the nulls near the main lobe disappear for the modulation index above a critical value. The peak level of the grating plateaus and their shapes are given in terms of approximate expressions and are exactly determined computationally. The nature of the curves suitable for design of such arrays for a given scan range and permissible peak sidelobe level is given. An example shows that a high resolution beam may be obtained with a comparatively smaller number of elements than required by a uniformly illuminated periodic array. An exact-series summation formula for the directivity of nonuniformly spaced antenna arrays of isotropic elements is given. The directivity of the modulated array computed by this formula shows a smooth variation at the ends of the scan range in contrast to the sudden fall in the case of the periodic array. View full abstract»

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  • Scattering by linearly vibrating objects

    Publication Year: 1979 , Page(s): 344 - 352
    Cited by:  Papers (15)
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    The scattering problem for a plane wave incident upon a perfectly conducting linearly oscillating object is investigated both theoretically and experimentally. The theoretical analysis, accurate to order v/c where v and c axe the velocities of object and light, respectively, shows that the target oscillation changes the scattered far field of a motionless target only in phase. The oscillation is assumed to be periodic, and this period is shown to be impressed on the scattered field. Spectral analysis of the modulation shows that the power distribution varies with the shape of the motion, wavelength of the incident field, and the magnitude of the projections of the oscillation in the direction of incidence and receiver. Power spectra have been calculated for square, triangular, and sinusoidal target motion and, in general, the power content in the higher harmonics is found to increase with cartier frequency and magnitude of oscillation. For backscattering from an object moving sinusoidally along the direction of incidence, the power in the first harmonic is shown to exceed that at the carrier frequency when d > 0.23\lambda where d is the magnitude of the oscillation. These calculations are shown to agree with experimental measurements of the phase modulation of the field scattered from a vibrating disk at the X -band. Experimental results were obtained with continuous wave backscatter equipment at 10 GHz that utilized separate tunnel antennas for transmitting and receiving. The receiving section of this equipment was modified to separately display phase modulation and amplitude modulation characteristics of the backscattered signal in both time and frequency, as well as characteristics of the overall modulation envelope. Phase modulations introduced by target oscillations as small as \pm 0.001 in were readily detected, as were amplitude modulations of a few percent. View full abstract»

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  • Useful experimental results for Earth-satellite rain attenuation modeling

    Publication Year: 1979 , Page(s): 413 - 415
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    Results pertaining to vertical profiles of rain rates derived from radar data as well as normalized cumulative probabilities of rain rates, which may be applicable over large areas of the world, are presented. We believe these results to be useful in the areas of earth-satellite rain attenuation modeling and prediction at frequencies above 10 GHz. View full abstract»

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  • Application of reflection and diffraction techniques to the analysis of an EMP simulator

    Publication Year: 1979 , Page(s): 353 - 356
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    The response of a parallel-plate transmission-line electromagnetic pulse (EMP) simulator to continuous wave excitation in the very high frequency (VHF) region is analyzed. A reasonably accurate prediction of response irregularities measured in an operational EMP test facility is obtained using a combination of geometrical optics and geometrical diffraction theory. The analysis predicts that multiple internal reflections were primarily responsible for observed irregularities at the measurement positions. While an analysis based upon optical techniques involves different approximations and assumptions than alternative methods, such as the method of moments, the optical approach was found to be more practical in the VHF regime and, perhaps more importantly, allowed identification of the dominant physical mechanisms which cause deviations from the ideal field quality desired of the facility in the VHF region. Based upon these calculations, the simulator was modified to reduce internal reflections, and subsequent measurements have confirmed the usefulness of the theoretical predictions. 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