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Antennas and Propagation, IEEE Transactions on

Issue 2 • Date March 1978

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  • [Front cover and table of contents]

    Publication Year: 1978 , Page(s): 0
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    Freely Available from IEEE
  • A note from the editor

    Publication Year: 1978 , Page(s): 197
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  • Emendation to "Correction to ́surface currents, scattering, and applications in the Rayleigh regioń "

    Publication Year: 1978 , Page(s): 366
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  • Comments on "Measured field of a directional antenna submerged in a lake"

    Publication Year: 1978 , Page(s): 366
    Cited by:  Papers (1)
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  • A variational method for efficient determination of SEM poles

    Publication Year: 1978 , Page(s): 354 - 358
    Cited by:  Papers (1)
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    A method is presented as an ancillary to the method of moments in computing the singularity expansion description of the transient response of a scatterer. The method is based on the variational character of a generalized Rayleigh quotient. The Rayleigh quotient approximation to the matrix eigenvalue which vanishes at a pole provides an alternative to the determinant as the objective of a zero search algorithm. The alternative is more economical to compute. It is necessary to have an estimate of the correct pole location in order to initiate the Rayleigh quotient procedure. Results of computational examples and suggestions of various ways through which one may estimate the pole location are presented. View full abstract»

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  • Characteristics of electromagnetic waves propagating in time varying media

    Publication Year: 1978 , Page(s): 358 - 361
    Cited by:  Papers (2)
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    Transform techniques are applied to obtain a solution describing the characteristics of electromagnetic waves propagating in media which are subject to abrupt time changes in permittivity. The case of a spherically expanding wave is considered in detail. The plane wave case is also discussed. Transform techniques provide a mechanism for easily extending the solutions through successive time changes. View full abstract»

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  • Design of corrugated conical horns

    Publication Year: 1978 , Page(s): 367 - 372
    Cited by:  Papers (45)  |  Patents (1)
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    Details of the design of circumferentially corrugated conical horns are presented. Radiation pattern and phase-center characteristics for both "wide-band" and "narrow-band" horns are considered, and a comparison is made between the relative sizes of the two types of horns. The effects of horn aperture size, slot width-to-pitch ratio and frequency on the cross-polarization of the radiation pattern are included. The range of slot parameters which can be used and the design of the slots near the throat of the horn to achieve a low VSWR for bandwidths of 1.5 to 1 are also considered. The results of measurements on horns with both narrow and wide included angles are given. View full abstract»

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  • Nonuniformly spaced linear and planar array antennas for sidelobe reduction

    Publication Year: 1978 , Page(s): 198 - 204
    Cited by:  Papers (15)  |  Patents (2)
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    The material discussed can be divided into two parts. In the first part, an iteration method is presented for calculating the distances between the elements of a symmetrical nonuniformly spaced linear array antenna for sidelobe reduction. The amplitude of the excitation is assumed to be constant. The iteration method is applied to linear array consisting of 24 elements. After a few iterations, the sidelobe-to-mainlobe power ratio was reduced to over 22 dB from its value of 13.2 dB for uniform array spacing. In the second part, several symmetrical nonuniformly spaced planar array antennas have been designed, using the nonuniform linear array spacings of part one. The planar arrays include square-shaped and circular structures, with the number of elements ranging from 284 to 576. The iteration method discussed can be applied to linear arrays with any number of elements to obtain nonuniform grid spacings for sidelobe reduction. A number of planar grid structures can be constructed using the nonuniform linear grids. The nonuniform linear and planar arrays utilize fewer radiating elements and result in desirable sidelobe structures. View full abstract»

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  • Measuring the gravitational astigmatism of a radio telescope

    Publication Year: 1978 , Page(s): 315 - 318
    Cited by:  Papers (5)
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    Most conventional radio telescopes will show a strong astigmatism when tilted, resulting in surface degradation, which can be corrected with a mechanically deformable subreflector. Astigmatism means different focal lengths ( \Delta F ) in two perpendicular planes. A most direct way of measuring the astigmatism is to measure \Delta F with an elongated rotatable feed, illuminating only a central strip of the telescope. Equations are given for the relations between \Delta F , rim deviation A , and rms surface deviation \Delta z , and for the dependence of these quantities on elevation angle. This method was applied to the 140-ft. telescope. Between zenith and horizon, the measured range is \Delta F = (51 \pm 2) mm, yielding an astigmatic rim deviation of A = 8.7 mm, and an astigmatic rms surface deviation of \Delta z = 2.87 mm. The latter agrees with astronomical efficiency measurements, showing that the total gravitational deformation is mainly of a simple astigmatic shape, to be corrected by relatively simple means. View full abstract»

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  • Approximate relationship between directivity and beamwidth for broadside collinear arrays

    Publication Year: 1978 , Page(s): 340 - 341
    Cited by:  Papers (4)
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    A simple approximate formula is given relating the directivity and beamwidth of broadside collineax arrays. View full abstract»

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  • A gain optimizing algorithm for adaptive arrays

    Publication Year: 1978 , Page(s): 228 - 235
    Cited by:  Papers (4)
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    An algorithm for optimizing the gain of an adaptive antenna on an incoming signal is discussed. The gain optimization is based on a constrained gradient-search technique. The algorithm is presented, and some examples are given. The convergence and stability of the algorithm are also discussed. View full abstract»

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  • Synthesis of a laterally displaced cluster feed for a reflector antenna with application to multiple beams and contoured patterns

    Publication Year: 1978 , Page(s): 220 - 228
    Cited by:  Papers (14)
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    When a feed is displaced from the focus of a reflector, phase distortion results in the effective aperture distribution, which in turn gives rise to secondary beam distortion. In multiple beam or contour beam antennas, the feed normally consists of an array of identical elements located on a triangular lattice. Taking advantage of this arrangement, a "cluster" of feed elements instead of a single element may be used to control each beam. By adjusting the relative excitations of the elements in a cluster, the aperture phase distortion due to the feed displacement may be partially compensated. Two general methods for synthesizing the excitations for a laterally displaced feed cluster are presented. In the first method the excitations are chosen to minimize the weighted phase error in the effective aperture by analytical means. The second method determines the excitations by a gradient optimization algorithm which minimizes the weighted error between an objective and the actual power patterns in the secondary pattern space. The first method is roughly two orders of magnitude more efficient computationally than the gradient optimization algorithm, but not as flexible in application or as precise. Numerical results are presented for cluster feed designs and their application to the synthesis of contour patterns. View full abstract»

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  • Atmospheric amplitude spectra in an absorption region

    Publication Year: 1978 , Page(s): 329 - 332
    Cited by:  Papers (12)
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    Amplitude spectra in the vicinity of the 60-GHz molecular oxygen resonant line are interpreted as a superposition of an absorption mechanism plus a scattering mechanism. Also, a simple derivation for the amplitude and phase spectra in the limit of small fluctuation frequencies is given. View full abstract»

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  • Ionospheric pulse time dispersion including effects of Earth's magnetic field

    Publication Year: 1978 , Page(s): 307 - 311
    Cited by:  Papers (3)
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    For frequencies above 100 MHz, the distortion due to ionospheric dispersion has been evaluated in the past for the assumption that the earth's magnetic field can be neglected. It is shown that for noncircularly polarized signals, conditions can exist at even L -band where the ionosphere distortion due to the presence of the earth's magnetic field can be significant. A simple expression relating the Faraday rotation to the ionospheric dispersion due to the earth's magnetic field is given. An example is presented which shows that the Faraday rotation can be as much as 145\deg at L -band. View full abstract»

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  • Experimental results on a linear array designed for asymmetric sidelobes

    Publication Year: 1978 , Page(s): 351 - 352
    Cited by:  Papers (2)
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    A nineteen element longitudinal shunt slot array was designed to give an input match and a sum pattern which is Taylor 20/20, except that the three innermost sidelobes on one side of the main beam are depressed to -30 dB. Experimental results are in good agreement with theory. View full abstract»

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  • Maximum likelihood estimation of the number, directions and strengths of point radio sources from variable baseline interferometer data

    Publication Year: 1978 , Page(s): 294 - 301
    Cited by:  Papers (5)
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    The optimum estimation of the number, directions, and strengths of multiple point radio sources is considered when the mutual coherence function of the sources' radiation is spatially sampled at M baselines by a variable baseline correlation interferometer. The measurements are corrupted by the effects of additive background noise (including receiver noise) and a finite correlation time. Statistically approached, the problem is considered as a combination of parameter estimation and goodness of fit with the maximum likelihood (ML) principle being the basic criterion used. First the measurements' probability density function is derived, assuming the sources' number is known. Then the ML estimator (MLE) of the sources' parameters is obtained. The MLE's asymptotic optimum performance (unbiasedness with minimum variance) is then shown to be achieved when the number of measurements exceeds the number of sources by a threshold that is small (or zero) for most signal-to-noise ratios of interest. Next the number of sources is estimated according to a likelihood probability that measures the tenability of the MLE associated with every possible number of sources with respect to the measurements. The ML number-parameter estimation theory is then put into the form of an efficient algorithm which proves to be superior when compared to other processing methods such as Fourier maps. View full abstract»

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  • Element pattern of dually polarized element in infinite phased array

    Publication Year: 1978 , Page(s): 347 - 350
    Cited by:  Papers (4)
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    Explicit relations for the pattern of both field components of a dually polarized element in an infinite phased array are established. Calculations of the radiated field are made for an infinite array of circular waveguide apertures for several lattices and scan planes. The computed results are compared with the analytically obtained patterns of an ideal element. The effect of cross polarization on the element patterns is shown for nonprincipal plane scans. View full abstract»

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  • Aperture performance of a double-ridge rectangular waveguide in a phased array

    Publication Year: 1978 , Page(s): 204 - 214
    Cited by:  Papers (4)
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    Despite its widely recognized broad-band characteristics, the potential of a double-ridge rectangular waveguide as a phased array element has not been systematically explored. An additional benefit in using this waveguide is its reduced size which permits realization of a compact array lattice for wide angle scanning applications. A number of treatments of ridge waveguide propagation characteristics appear in the literature [1] -[5], but an analysis of the performance of a double-ridge waveguide phased array element has only recently been published [6], [7]. The results presented are based on [6], but they include additional material. The unmatched aperture performance of a rectangular ridge-guide in a number of wide-band phased arrays with quarter-hemispherical coverage, and a single narrow-band H -plane scan design are examined. A parametric study and comparison of the unmatched aperture performance of a ridged-guide element with that of a rectangular waveguide reflects the capabilities of the double ridged-guide wide-band element in a large phased array. Such parametric study reveals to the designer the active admittance of the unmatched radiating element and leads in a systematic manner to a choice of the ridge-guide geometry and array lattice, to be followed by the determination of a suitable matching structure. This approach contrasts that of [7], which concentrates on demonstrating the feasibility of broad-band matching of a particular dual ridged-element. View full abstract»

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  • Radiation from a wide-angle conical horn with a homogeneous dielectric sphere in front of its aperture

    Publication Year: 1978 , Page(s): 363 - 365
    Cited by:  Papers (1)
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    The effects of placing a homogeneous dielectric sphere in front of the aperture of a wide-angle conical horn are studied both theoretically and experimentally. The theoretical formulation of the ratiation characteristics of the device is made on the basis of scattering of electromagnetic waves by a dielectric sphere. The calculations based on this formulation show overall agreement with the experimental radiation pattern and directivity measurements. It is concluded that the dielectric sphere mounted conical horns will have directiveities in excess of that obtained with a conventional conical horn of the same dimensions, and also that the device can be used as a variable beam feed for parabolidal reflectors. View full abstract»

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  • The design of small slot arrays

    Publication Year: 1978 , Page(s): 214 - 219
    Cited by:  Papers (61)
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    The differences in mutual coupling for a central slot and a peripheral slot cannot be ignored in small arrays if good patterns and impedance are to be obtained. A theory has been developed whereby the length and offset of every slot in the array can be determined, in the presence of mutual coupling, for a specified aperture distribution and impedance match. The theory enlarges on Stevenson's method, and uses a modified form of Booker's relation based on Babinet's principle to treat nonresonant longitudinal shunt slots in the broad wall of a rectangular waveguide. A general relation between slot voltage and mode voltage is developed, and then formulas are derived for the active, self-, and mutual admittances among slots. These formulas result in a design procedure. Analogous treatments of inclined series slots in rectangular guide and of strip-line-fed slots are possible. Comparison between various experiments and the theory is presented. Tests of the theory include the resonant length of a zero offset slot, resonant conductance versus offset and resonant conductance versus frequency for a single slot, and self- and mutual admittances for two staggered slots. The design and performance of a two-by-four longitudinal shunt slot array is also described. View full abstract»

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  • Microwave holography by rotational scanning of object

    Publication Year: 1978 , Page(s): 280 - 281
    Cited by:  Papers (1)
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    A rotational scanning technique useful in microwave holography is developed. This technique has the special feature that the recording structure can be constructed on a smaller scale than a conventional scanning technique, and that a lensless Fourier transform hologram is obtainable. The theoretical aspect of this new holographic arrangement and experimental evidence in support of the theory are presented. View full abstract»

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  • Input impedance of a monopole antenna at the center of a finite ground plane

    Publication Year: 1978 , Page(s): 244 - 248
    Cited by:  Papers (20)
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    A technique for computing the input impedance of a monopole on a finite ground plane is provided. The case of an infinite ground plane is first examined, and then the concept of using a magnetic edge current as an equivalent source of diffraction on the limited size ground plane is introduced. The technique used is serf-consistent in that the circular ground plane considered is the limit of a polygonal ground plane as the number of sides tends to infinity. Good agreement has been demonstrated when the nearest edge of the ground plane is at least 0.3 wavelength from the base of the monopole. View full abstract»

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  • Scattering by multilayered lossy periodic strips with application to artificial dielectrics

    Publication Year: 1978 , Page(s): 257 - 260
    Cited by:  Papers (4)
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    The scattering properties of multiple-layered interfaces each comprising metal strips periodically mounted on a lossy dielectric substrate are examined. The formulation employs the impedance sheet concept extended to multiple-layered periodic interfaces. The solution yields the currents as well as the transmitted and reflected fields. It is found that convergence is rapid, and the solution numerically stable. Results have been obtained for up to nine layers. By matching the complex transmitted and reflected fields to an actual dielectric slab, it is also possible to determine the refraction index and effective loss tangent of a strip-type artificial dielectric. Results thus obtained exhibited excellent agreement in refraction index with measurement and other theory when the medium is lossless. Moreover, it also now allows not only the quantitative examination of losses in artificial dielectrics but also the refraction index sensitivity to substrate thickness. View full abstract»

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  • On the design of an N × N element uniform planar array

    Publication Year: 1978 , Page(s): 344 - 345
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    Maximum directivity curves are presented to enable an easy and efficient design of a uniform planar array of N \times N directive elements. View full abstract»

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  • Atmospheric structure, transhorizon propagation, and their relationship to remote sensing

    Publication Year: 1978 , Page(s): 333 - 340
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    Previous papers suggest that the characteristics of atmospheric structure cannot be inferred unambiguously from transhorizon scatter measurements. It is shown that the form of the refractivity spectrum can be correctly inferred from appropriate beam-swinging measurements. One analysis includes contributions from both scattered and partially reflected components of the transhorizon signal, and shows how the characteristics of the angular response pattern of the received signal varies with changes in these components. Analytically derived patterns are compared with measured response patterns. The form of the refractivity spectrum inferred from the comparison is consistent with the form suggested from physical arguments and by the results of independent transhorizon experiments. Because the transhorizon signal includes scattered and partially reflected signals, remote-sensing techniques using transhorizon methods should employ both signal components to correctly derive atmospheric parameters. Finally, both of these signal components should be used for channel models that use adaptive algorithms to optimize the design of troposcatter communication networks. 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