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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date July 1985

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  • [Front cover and table of contents]

    Publication Year: 1985 , Page(s): 0
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    Freely Available from IEEE
  • Defocusing loss for a log periodic-fed reflector

    Publication Year: 1985 , Page(s): 809 - 812
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    Log periodic designs are a well established wide-band antenna technology, but one in which the phase center travels along the structure as the frequency varies. When a log periodic antenna is used as a feed for a reflector antenna, the phase center location cannot be maintained at the reflector focus over the frequency range and defocusing results. The purpose of this analysis is to quantify the defocusing loss for a log periodicfed reflector. The analysis presented compares favorably with measured results. View full abstract»

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  • Measurement of the electrical constitutive parameters of materials using antennas

    Publication Year: 1985 , Page(s): 783 - 792
    Cited by:  Papers (18)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    A general technique is presented for measuring the electrical constitutive parameters of a material using a monopole (dipole) antenna. A normalized impedance that is only a function of the dimensionless parameter kh (wavenumber length) is defined for the antenna. The normalized impedance is expressed as a rational function, and the coefficients in this function are determined from a measurement of the impedance in a standard medium. The impedance measured in a material with unknown constitutive parameters is used with the rational function to form a polynomial in kh . The constitutive parameters of the medium are determined from a root of this polynomial. The measurement technique is implemented for a rational function of order three. The constitutive parameters of the alcohol 1-butanol and saline solutions were measured over a range of frequencies using the technique with cylindrical and conical monopole antennas. The measured constitutive parameters are in good agreement with those determined by previous investigators. View full abstract»

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  • Whitening of sidelobe powers by pattern switching in radar array antenna

    Publication Year: 1985 , Page(s): 727 - 735
    Cited by:  Papers (3)
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    Presented here is a concept for nearly eliminating bias errors in reflectivity and velocity estimates due to power received through antenna sidelobes of pulse Doppler radars. The antenna pattern is switched from pulse to paise among specially designed patterns, with near identical main lobes, but with sidelobes having randomly distributed phases and amplitudes. The sidelobe signal then becomes incoherent without affecting the coherency of the main lobe signal. The whitened sidelobe signal does not bias the mean velocity estimate computed by Doppler processing, and an unbiased estimate of reflectivity can be computed with the knowledge of the mean whitened power level. Pattern design criteria and a method for the design of optimum patterns are developed for a linear array. The extent of sidelobe reduction by way of whitening has been studied in detail for special case of only two patterns switched randomly using a pseudonoise sequence. Pattern switching realizes an effectively low sidelobe pattern without sacrifice of main lobe resolution. A possible extension to two-dimensional arrays is suggested. View full abstract»

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  • Neighboring-patch integrals in transient electromagnetic scattering

    Publication Year: 1985 , Page(s): 768 - 773
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    The integrals over patches that are close to the self-patch are calculated by expanding the factors in the integrand in power series. The values are computed analytically up to first order in the linear size of the patch. This procedure applies to patches for which the distance between the centers is of the same order of magnitude as the size of the patch. The same formulas are useful in steady-state scattering problems. View full abstract»

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  • Electromagnetic scattering from appendages on a smooth surface

    Publication Year: 1985 , Page(s): 736 - 743
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    A solution is obtained for the high frequency backscattered far field from appendages such as an inlet mounted on arbitrary smooth surfaces. The goal here is twofold; first, to demonstrate the effectiveness of the uniform geometrical theory of diffraction (UTD) in computing the scattered fields from such complex targets, and second, to develop iterative techniques to find multiply diffracted ray paths to be used in the application of UTD. These techniques are applicable to numerically as well as analytically defined surfaces. View full abstract»

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  • A graphical technique for determining optimal array antenna geometry

    Publication Year: 1985 , Page(s): 719 - 726
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A new graphical technique is presented for determining the optimal face tilt and element packing geometry for planar, phased-array antennas with scan limits specified in earth's coordinates. The technique, although very simple to implement, is instructive in that it clearly shows, on one graph, the relationships between required azimuth and elevation scan limits, the element packing geometry, the grating lobe locations, grating lobe scan boundaries, the maximum off-axis scan angle, and the array face tilt angle. The technique can be used to design the array to either minimize the maximum scan off-axis scan requirement or to minimize the total number of elements in the array. Examples are presented that clearly show the two designs are not the same. It is shown that the grating lobe scan boundary (GLB) for a particular array geometry can easily be constructed in sine-space by drawing unit circles centered at six grating lobe locations nearest to the origin of the sine-space plane. Equations are presented for drawing the required scan boundary (RSB) in earth's coordinates for the array with its face tilted back from the vertical. The ability to simply construct the RSB and GLB on the same sine-space plot makes it very simple to choose the tilt angle and element geometry that either minimizes the area in the GLB or the maximum off-axis scan requirement for a given RSB. View full abstract»

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  • Inverse black body radiation: An extant closed-form solution

    Publication Year: 1985 , Page(s): 797 - 800
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The inverse black body radiation problem, concerned with the determination of the temperature distribution of a block body source from spectral measurements, has recently been formulated. Here, an exact closed-form reconstruction algorithm is given in terms of on infinite series. This algorithm, which avoids iteration, can be implemented either numerically or analytically. The method is applied to several analytical and numerical examples with excellent results. View full abstract»

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  • Complex polynomial phase integration

    Publication Year: 1985 , Page(s): 800 - 805
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    A previously published integration algorithm applicable to the numerical computation of integrals with rapidly oscillating integrands is generalized. The previous algorithm involved quadratic approximation of the phase function which was assumed to be real. The present generalization concerns approximation of a complex phase function by a polynomial of arbitrary degree. As before, the integrand is then written without approximation as a slowly varying function multiplied by the polynomial phase exponential and the slowly varying factor is approximated by a finite sum of Chebyshev polynomials. The integral is thus expressed as a sum of constituent integrals which are computed recursively via LU decomposition applied to a system of linear equations with a banded coefficients matrix. Examples are presented comparing various degree phase approximants. View full abstract»

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  • A wavefront interpretation of the singularity expansion method

    Publication Year: 1985 , Page(s): 706 - 718
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1336 KB)  

    The singularity expansion method (SEM) represents transient scattering by superposition of damped oscillatory fields corresponding to the complex resonant frequencies of the scatterer. The series of these global wave fields, which encompass the scattering object as a whole, is slowly convergent at early observation times and even deficient at very early times when portions of the object are as yet unexcited. Thus, the resonance series representation must generally be augmented by an entire function in the complex frequency domain. The choice of the entire function is relatively arbitrary but affects the excitation coefficients, called coupling coefficients, of individual resonances and also the "turn-on" and "switch-on" times of the SEM series. Moreover, it contains essential (intrinsic) and nonessential (removable) portions which have been subjected to various interpretations. By formulating the transient problem in terms of traveling (progressing) incident, reflected and diffracted wavefronts, these constructs in the SEM can be interpreted in a precise and physical manner. Furthermore, the analysis clarifies the evolution of resonances as collective summations of multiple wavefront fields which are caused by successive reflections or diffractions at the surfaces and scattering centers comprising the object. By combining wavefronts and resonances self-consistently, one may construct a hybrid field that avoids the difficulties at early times in the SEM formulation. The systematic exploration of the interplay between wavefronts and resonances is facilitated through use of a flow diagram, as introduced in system theory. These concepts are developed in broad generality and are illustrated for two-dimensional scattering by various special configurations. View full abstract»

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  • Self-patch integrals in transient electromagnetic scattering

    Publication Year: 1985 , Page(s): 763 - 767
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The self-patch integrals that arise in the integral equations of electromagnetic scattering are evaluated analytically for general orthogonal coordinate systems to first order in the linear size of the patch. There are terms that contain spatial derivatives of the surface fields, and these terms may not be negligible. Although the formulas are derived for transient waves, the same integrals appear for monochromatic waves. View full abstract»

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  • The scattering behavior of a slightly rough surface moving parallel to its mean plane with uniform velocity

    Publication Year: 1985 , Page(s): 793 - 796
    Cited by:  Papers (1)
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    The scattering of plane electromagnetic (EM) waves from a perfectly conducting, slightly rough surface moving in vacuum with uniform and constant velocity is examined by combining the boundary perturbation method and the special, homogeneous Lorentz transform. The direction of motion is assumed to be parallel to both the incidence plane and the mean plane of the moving rough surface. The analysis is confined to first-order scatter. The end result is the determination of the velocity-dependent expressions for the bistatic and backscatter incoherent cross sections per unit area of the scattering surface. The expressions for bistatic geometry are only valid for scattering inside the plane of incidence. A numerical example demonstrates the effect of the motion on the scattering behavior of the rough surface. View full abstract»

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  • TM scattering by a dielectric cylinder in the presence of a half-plane

    Publication Year: 1985 , Page(s): 773 - 782
    Cited by:  Papers (18)
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    The problem considered is the transverse magnetic (TM) scattering by a dielectric cylinder in the presence of a perfectly conducting half-plane. An integral equation, involving the half-plane Green's function in its Kernel, is obtained for the equivalent volume currents representing the dielectric cylinder. This integral equation is solved by the method of moments. Numerical results are compared with measurements for the echo width of a dielectric slab on a half-plane. The dielectric slab surface impedance and the fields inside the dielectric are also shown. View full abstract»

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  • The Luneburg-Kline expansion determined from bandlimited scattering data

    Publication Year: 1985 , Page(s): 805 - 809
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    A method for determining the coefficients of an asymptotic 1/\omega -expansion, known as Luneburg-Kline expansion, from bandlimited scattering data is presented. The coefficients are derived from the output signals of an orthogonal filter. The method is applicable to calculate geometric quantities as principal radii or principal directions of curvature of simple scatterers. Furthermore early parts of transient backscattered signals can be analyzed, e.g., to reconstruct the early ramp or impulse response. View full abstract»

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  • Dielectric image line groove antennas for millimeter waves, Part II: Experimental verification

    Publication Year: 1985 , Page(s): 697 - 706
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB)  

    In the first part of this paper the theory of radiation from discontinuities in the ground plane of a dielectric image line has been described. In this second part experimental verifications of the radiation theory as well as millimeter-wave antennas realized on the basis of the theory are described. In the antennas slots and holes in the ground plane of the dielectric image line are used as discontinuities. Experimental results for the radiation characteristics are discussed. View full abstract»

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  • Dielectric image line groove antennas for millimeter waves, Part I: Theoretical background

    Publication Year: 1985 , Page(s): 690 - 697
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    Dielectric image line groove antennas are very useful for the application in the millimeter-wave region. In this first part of a two-part paper, three different types of groove discontinuities under a dielectric image line for application in millimeterwave antennas are investigated: the equivalent circuits of 1) a slot discontinuity in a metallic ground plane and 2) a slot discontinuity in the metallization of a substrate material under a dielectric image line are derived theoretically using an approximation for the electromagnetic fields of the slots. 3)The equivalent circuit of cylindrical holes in a metallic ground plane under a dielectric image line is derived from measurements. The results are used to synthesize millimeterwave dielectric image line antenna arrays as described in part II of the paper. View full abstract»

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  • Phase retrieval in the radio holography of reflector antennas and radio telescopes

    Publication Year: 1985 , Page(s): 749 - 755
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    Methods of phase retrieval from simulated intensity information have been tested for use in the radio holography of reflector antennas. In numerical simulations the Misell algorithm has been used successfully to retrieve the aperture phase distribution from two numerically simulated power polar diagrams, one in focus and the second defocused. The technique uses no auxilliary reference antenna. However, it does need a high signal to noise ratio, typically 50 dB if a 60 \times 60 array is to be measured to a precision such that the gain is within 1 percent of ideal. It should be most useful where no direct phase measurements are possible and ground-based or satellite transmitters can be used as sources. The use of astronomical maser sources (22 GHz) can give information on large scale deformations. View full abstract»

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  • Siting of Doppler weather radars to shield ground targets

    Publication Year: 1985 , Page(s): 685 - 689
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    Weather radars are usually sited so they can survey as large an area as possible. A large surveillance area is achieved by placing the antenna as high as practical but then the radar can be blind to weather targets near the ground because of ground clutter interference. There are applications where it is necessary to have fine resolution of low altitude divergence and wind shear near the ground in regions of weak weather reflectivity. This requirement can be most conveniently satisfied when surveillance is near the radar, but it brings attention to the problem of reducing ground clutter. Although cancelers help to reduce ground target echoes, they cannot eliminate them, and reduction for scanning beams is limited to about 40 dB. Proper siting to take advantage of natural terrain and man-made shields (clutter fences) can further reduce ground clutter. Criteria are developed that relate ground target illumination to antenna characteristics, shield heights, and the distance to the shield. Both geometric optic and diffraction theory are used to estimate the effectiveness of shields. View full abstract»

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  • Parabolic antennas with a loaded flange

    Publication Year: 1985 , Page(s): 755 - 762
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The radiation characteristics of a parabolic dish with a loaded peripheral flange are examined in detail in order to assess the effectiveness of such a loading in further reducing the backward scattered field. Uniformly valid diffraction coefficients are developed to deal with both isotropic and anisotropic surface impedances. It is shown that substantial improvement of the antenna performance can be obtained in a wide rear angular sector, and the optimal loading conditions are determined. View full abstract»

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  • Focal shifts in parabolic reflectors

    Publication Year: 1985 , Page(s): 744 - 748
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    Given a parabolic reflector, the maximum directivity is not always achieved by placing the feed at the focal point. Depending on the nature of the feed, the maximum directivity can be obtained by axially displacing the feed either toward or away from the reflector. For low-tapered feeds, the shift should be toward the reflector. This result is similar to an optical phenomenon called the focal shift. We find that this positive shift depends mainly on the Fresnel number of the reflector. For highly tapered feeds, the shift should be away from the reflector. This negative shift becomes significant when the reflector aperture is small, in units of wavelength. A unified view is presented to explain both the positive shift and the negative shift in terms of spillover, aperture illumination efficiency and phase asynchronism. For a system with optimum aperture edge taper, no focal shift can exist. 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