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Antennas and Propagation, IEEE Transactions on

Issue 8 • Date August 1985

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Displaying Results 1 - 21 of 21
  • [Front cover and table of contents]

    Publication Year: 1985 , Page(s): 0
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    Freely Available from IEEE
  • Comments on and extensions to "Evaluation of Fourier integrals using a FFT with improved accuracy and its applications"

    Publication Year: 1985 , Page(s): 924 - 926
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    The evaluation of Fourier integrals using fast Fourier transform (FFT) employing the Narasimhan scheme is examined. It is observed to be a special case of spline interpolation. His method is effective when the sampling rate is sufficiently high and piecewise linear approximation between sampling points is adequate. If knowledge about the signal smoothness is available, further improvement in accuracy can be achieved by judicious choice of high degree spine interpolant. View full abstract»

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  • On the multilook images of moving targets by synthetic aperture radars

    Publication Year: 1985 , Page(s): 823 - 827
    Cited by:  Papers (27)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    In the multilook processing of synthetic aperture radar (SAR) data, subapertures are synthesized at different center times so that a time-lapse exists between looks. This does not affect the imaging of stationary targets but if targets are in motion, the information content about the targets differs from look to look. The purpose of this paper is to investigate the effects of motions on the SAR multilook images of moving targets. Expressions are derived for the impulse response function from a moving point target in terms of the look number and the nature of the motion. Discussions are given only on the effects inherent to multilook processing. View full abstract»

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  • Anisotropic dielectric properties of media containing aligned nonspherical scatterers

    Publication Year: 1985 , Page(s): 886 - 890
    Cited by:  Papers (1)
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    Electromagnetic wave propagation in a medium containing a random distribution of aligned, pair-correlated nonspherical scatterers is studied using the T -matrix to characterize the single scatterer response, the quasicrystalline approximation (QCA) and the correlation function. The resulting dispersion equation for the average medium is numerically solved as a function of frequency and the direction of propagation. Numerical results are presented for the attenuation of electromagnetic waves versus frequency, concentration, and direction of propagation. View full abstract»

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  • Reducing grating lobes due to subarray amplitude tapering

    Publication Year: 1985 , Page(s): 846 - 850
    Cited by:  Papers (23)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    Subarray amplitude tapering is a simple, lower cost method to generate low sidelobes in an antenna's far-field pattern. Unfortunately, this simple technique also generates unwanted grating lobes. Placing the exact amplitude taper at the element outputs produces the desired far-field pattern, but the feed architecture is complicated and expensive. An alternative to these two techniques is described. A trade-off exists between sidelobe performance and simplicity of design. This trade-off consists of amplitude tapering the subarray outputs and the element outputs in such a way that the element amplitude tapers are identical for every subarray. In this way, the amplitude taper approximates the desired taper much better than subarray tapering alone, yet all the subarrays are identical. Thus, the feed design remains very simple. View full abstract»

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  • Half-plane diffraction in a gyrotropic medium

    Publication Year: 1985 , Page(s): 813 - 822
    Cited by:  Papers (2)
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    The diffraction problem of a plane wave obliquely incident on a half-plane embedded in a gyrotropic medium whose distinguished axis is parallel to the haft-plane's edge is considered. The problem is a generalization of previous work by Jull who treated normal incidence of a plane wave. The generalization is not trivial: indeed for many years the problem had been thought insoluble. We have found that the Wiener-Hopf-Hilbert (WHH) method provides a factorization of the Wiener-Hopf maxtrix encountered, and we obtain an exact closed-form solution. View full abstract»

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  • Analysis of a suspended patch antenna excited by an electromagnetically coupled inverted microstrip feed

    Publication Year: 1985 , Page(s): 895 - 899
    Cited by:  Papers (7)
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    A suspended patch antenna electromagnetically excited by an inverted microstrip line has been studied based on a full-wave transmission line analysis in conjunction with a microwave network theory. The input impedance calculated has been compared with measured data. View full abstract»

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  • A uniform GTD formulation for the diffraction by a wedge with impedance faces

    Publication Year: 1985 , Page(s): 867 - 873
    Cited by:  Papers (55)
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    A uniform high-frequency solution is presented for the diffraction by a wedge with impedance faces illuminated by a plane wave perpendicularly incident on its edge. Arbitrary uniform isotropic impedance boundary conditions may be imposed on the faces of the wedge, and both the transverse electric (TE) and transverse magnetic (TM) cases are considered. This solution is formulated in terms of a diffraction coefficient which has the same structure as that of the uniform geometrical theory of diffraction (UTD) for a perfectly conducting wedge. Its extension to the present case is achieved by introducing suitable multiplying factors, which have been derived from an asymptotic evaluation of the exact solution given by Maliuzhinets. When the field point is located on the surface near the edge, a more accurate asymptotic evaluation is employed to obtain a high-frequency expression for the diffracted field, which is suitable for several specific applications. The formulation described in this paper may provide a useful, rigorous basis to search for a more numerically efficient but yet accurate approximation. View full abstract»

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  • Analysis of time domain scattering by a flat plate

    Publication Year: 1985 , Page(s): 917 - 922
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    A numerical modeling technique is developed to calculate time-domain responses for a range which radiates short pulse signals. The theoretical time domain response for the case of bistatic scattering by a finite flat plate is calculated by combining frequency data from uniform geometrical theory of diffraction (UTD) and moment method (MM) solutions. The theoretical responses are compared to measured time waveforms showing good agreement. View full abstract»

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  • Surface accuracy of Cassegrain antennas

    Publication Year: 1985 , Page(s): 828 - 837
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    For a Cassegrain antenna system, a simple and general procedure is presented for computing the effective surface root mean square (rms) and beam deviations considering primary surface distortions and relative translations and rotations of the antenna components. It is shown that certain primary reflector distortions can be compensated for by an appropriate adjustment of the subreflector position. Different methods in use for calculating surface rms are reviewed. It is shown that the method in which the deformed configuration of the primary reflector is best fitted with another paraboloid yields a surface rms almost equal to that obtained by the optimal positioning of the antenna components. The actual deformation patterns of several large Cassegrain antenna systems with different structural concepts are reviewed. It is shown that for a class of antenna structures, the gain can be significantly improved by an optimal positioning of the subreflector. View full abstract»

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  • On the gain maximization of a dual frequency and direction array consisting of wire antennas

    Publication Year: 1985 , Page(s): 874 - 880
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    A dual frequency and dual directional antenna is an antenna with maximum gain in two different directions for two different frequencies. Maximum gain will be reached by the matrix method. This will be applied for two different situations. In the first we maximize the gain at one frequency and one direction under the constraint that the gain at the other frequency and direction has a given value. In the second we maximize the gain at one frequency and one direction under the constraint that it has a given relation with the gain in the other. A comparison between the two methods shows some practical considerations. View full abstract»

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  • Correction scheme for continuous rotation of the test antenna using fast near-field measurement techniques

    Publication Year: 1985 , Page(s): 922 - 924
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    A correction procedure is developed for the case of the continuous rotation of test antenna while performing fast near-field measurements. This general development is vital for the technique of modulated scattering which combines fast electronic scanning through the use of a probe array in one dimension and the rotation of the test antenna for the other dimension. A numerical simulation was performed to check the validity of the correction procedure. The correction procedure is not based on any interpolation scheme. View full abstract»

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  • Factorization of the feed efficiency of paraboloids and Cassegrain antennas

    Publication Year: 1985 , Page(s): 903 - 908
    Cited by:  Papers (55)
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    The first approximation to the aperture efficiency of a paraboloidal reflector antenna is called the feed efficiency. The factorization of the feed efficiency into subefficiencies which account for losses due to spillover, cross polarization, nonuniform aperture illumination, and phase errors is considered. The relations between the radiation patterns of circularly and linearly polarized feeds are also derived. View full abstract»

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  • Characteristics of sea reflection fading in maritime satellite communications

    Publication Year: 1985 , Page(s): 838 - 845
    Cited by:  Papers (12)
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    The Japanese domestic experimental mobile satellite system (EMSS) has been studied to establish high quality channels for small vessels with compact and low-gain antennas. The present international maritime satellite communication system (INMARSAT) has also been studied for the next generation to extend services for small ships, for which the present ship terminals including the antenna systems are too large and too heavy. By using a low-gain antenna, however, multipath fading caused by sea reflections will become a serious problem in designing the new system. To take effective countermeasures to the fading effect, it is very important to get a better knowledge of the fading phenomena caused by sea reflections. From a standpoint of maritime satellite communications, experiments measuring the amount of fading were performed under various sea conditions and in two frequency bands. The wave height, which is considered the most important experimental parameter, was measured objectively by a wave rider buoy. The experimental results show that the amount of fading depends on a wave height and radio frequency and, as the most interesting result, as a wave increases above a certain level, the amount of fading decreases. These results are also discussed theoretically. View full abstract»

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  • A hybrid technique for analyzing wire antennas in the presence of a plane interface

    Publication Year: 1985 , Page(s): 881 - 885
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    A hybrid technique which combines the method of moments (MM) with ray methods is employed to analyze the radiation of wires in the presence of a plane interface. In this technique, which is an extension of that proposed for combining the MM with the uniform geometrical theory of diffraction (GTD), a piecewise sinusoid (PWS) Galerkin method formulation is used. In this paper the basic assumption is made that a PWS dipole can be replaced by three sources of transverse, spherical waves, so that their fields can be treated separately by standard ray methods. Via this procedure the MM matrix can be easily augmented to account for the wire-interface interactions. Calculations of the field both radiated in the antenna half-space and transmitted through a plane interface are found in very good agreement with those performed by using the rigorous Sommerfeld integral representation. These results show that this technique provides an accuracy which is widely acceptable in most engineering applications, even when the wire is placed very close to the interface. This approach, which employs ray methods to calculate reflected and transmitted field contributions, appears promising to treat the case of curved interfaces. View full abstract»

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  • A wide-band corner-reflector antenna for 240 to 400 MHz

    Publication Year: 1985 , Page(s): 891 - 892
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    The design and performance characteristics of a corner-reflector antenna capable of operation in the 240 to 400 MHz frequency range are described. The corner reflector is suitable for use as a standard reference antenna for wide-band swept-frequency gain measurements. Measured voltage standing-wave ratio (VSWR), gain, and patterns are presented. View full abstract»

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  • Polarization losses in reflector antennas

    Publication Year: 1985 , Page(s): 899 - 903
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    Various definitions for polarization-loss efficiency of Cassegrainian and front-fed reflectors are compared. The effects of flare angle, feed taper and the feed pattern asymmetry on the polarization-loss efficiency are investigated. The definitions based on aperture fields are shown to be inadequate and far fields must be used for calculating the polarization losses. View full abstract»

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  • Field singularities at the tip of a dielectric cone

    Publication Year: 1985 , Page(s): 893 - 895
    Cited by:  Papers (2)
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    Data are given on the nature of the singularities near the tip of a dielectric cone of circular cross section. For a "sharp" cone the singularity is associated with a \varphi -independent potential; for a "reentrant" cone with a " \cos \varphi " type of potential. View full abstract»

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  • Transport of the mutual coherence functions and the intensity of a backscattered pulse in a random medium

    Publication Year: 1985 , Page(s): 851 - 859
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    Starting with a Helmholtz wave equation, the transport equations for the coherent and incoherent parts of the two-frequency two-position mutual coherence function in the transform domain can be derived. These equations have their respective analogs in the conventional radiative transfer theory. By solving the equations for the coherent part and the incoherent part, the incoherent scattered intensity is expressed as an infinite series, each term of which can be interpreted as an " n th order" scattered contribution. A procedure is given to compute the effective wavenumber and the total cross section, starting from a proper form of the mean Green's function. The intensity of a backscattered pulse is next investigated. A series expression is obtained. In order to be able to localize the position of pulse returns, "higher order" scattering terms must not be important when compared with the "single" scattered pulse. Numerical examples, applicable to the microwave scattering, show that the backscattered intensity is reduced when it is compared with the Booker-Gordon formula, even when the mean-square dielectric fluctuation is very small. This reduction is attributed to the multiple scattering effects, especially the multiple large-angle scatterings. View full abstract»

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  • Adaptive sidelobe cancellation of wide-band multipath interference

    Publication Year: 1985 , Page(s): 908 - 917
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    The steady-state performance of a narrow-band sidelobe canceller using a single auxiliary element with tapped delay line is analyzed for a simple two-path interference model, and an impulse response model is developed to provide insight as to the cancellation performance that might be expected. Computer solutions are then presented for various combinations of signal and multipath parameters. It is shown that auxiliary delay taps are required for effective cancellation of wide-band multipath interference, even for fractional bandwidth-delay products. Good cancellation is generally achieved provided that 1) the delay line taps are spaced much closer than the Nyquist sampling rate, and 2) the total length of the delay line considerably exceeds the longest multipath delay, depending on multipath component strengths. View full abstract»

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  • Evaluation of reflected fields at caustic regions using a set of GO equivalent line currents

    Publication Year: 1985 , Page(s): 860 - 866
    Cited by:  Papers (2)
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    A set of equivalent electric and magnetic line currents is derived which supplements the geometrical optics (GO) solution in the far zone whenever one of the surface principal radii becomes very large. These hypothetical currents lie along the specular line of the surface and are shown to produce the same result as the stationary phase contribution of the physical optics integral. An example of a systematic application of such equivalent currents for the computation of the scattered field from a complex structure is also demonstrated. 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