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Antennas and Propagation, IEEE Transactions on

Issue 9 • Date September 1984

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Displaying Results 1 - 25 of 26
  • [Front cover and table of contents]

    Publication Year: 1984 , Page(s): 0
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  • Electromagnetic transmission through mesh covered apertures and arrays of apertures in a conducting screen

    Publication Year: 1984 , Page(s): 908 - 913
    Cited by:  Papers (5)
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    The problem of electromagnetic transmission through wire mesh covered arbitrarily shaped aperture or arrays of apertures (possibly covered by a thin lossy dielectric sheet) in a perfectly conducting ground plane is considered. The equivalence principle and image theory are used to derive an integral equation for the equivalent magnetic currents. The method of moments is utilized to solve the integral equation, with the aperture modeled by triangular patches. Numerical results are presented for transmission coefficients and transmission cross-section patterns for electrically small apertures. View full abstract»

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  • Experimental determination of resonant frequencies by transient scattering from conducting spheres and cylinders

    Publication Year: 1984 , Page(s): 914 - 918
    Cited by:  Papers (5)
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    A new experimental technique to measure resonant frequencies of a target is presented. A Tektronix WP 1310 waveform processing system has been employed, which features signal processing software with extensive control over instruments, waveform manipulations, and graphic display. Numerous transient waveforms scattered from spheres and cylinders of various sizes have been recorded. A recently developed data-processing technique has been described and applied to these transient waveforms to extract their resonant frequencies. With the use of a new window designed to have a low near-sidelobe level, the modified fast Fourier transform (FFT) is shown to be able to improve the measurement capability of the system. View full abstract»

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  • Comments on "First-order equivalent current and corner diffraction scattering from flat plate structures"

    Publication Year: 1984 , Page(s): 1011 - 1012
    Cited by:  Papers (4)
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  • Correction to "Forward scattering from cylinders of triangular cross section"

    Publication Year: 1984 , Page(s): 1011
    Cited by:  Papers (4)
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  • Design of shaped-beam antennas through minimax gain optimization

    Publication Year: 1984 , Page(s): 963 - 968
    Cited by:  Papers (12)  |  Patents (2)
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    An essential part of realizing a shaped beam by using a multiple-beam antenna is determining the excitation coefficient for each individual port. An algorithm which optimizes the power gain in a minimax sense is described. This criterion, although not as mathematically tractable as least squares, is necessary when the specifications prescribe that the worst case be as good as possible. It will be shown how the basic algorithm is very efficient and how it permits simple modifications to allow the specification of one-sided errors for the pattern, and direct optimization of gain slopes. A design of a C-band shaped-beam satellite antenna provides an example. View full abstract»

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  • Aperture efficiency for paraboloidal reflectors

    Publication Year: 1984 , Page(s): 997 - 1000
    Cited by:  Papers (5)
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    The definition and formulas for cross polarization, phase error, and illumination efficiency given by Ludwig and Thomas are shown to not always account for the correct cross polarization and phase error loss. New definitions and formulas are proposed that give a better separation of the losses associated with cross-polarized radiation, phase errors, and nonuniform aperture illumination. View full abstract»

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  • Scanning of sector and cosecant beams generated by a circular aperture

    Publication Year: 1984 , Page(s): 1000 - 1003
    Cited by:  Papers (2)
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    A method of scanning a one-dimensional shaped pattern generated by a circular aperture is presented. It is shown that the desired beam shape can be retained in the desired scan plane by superposing on the nonlinear phase distribution applied along and parallel to the meridian plane, a linear phase progression along the perpendicular direction. Analysis carried out using the stationary phase method of evaluating the integral reveals that the gradient of the linear phase progression is a function of position along the meridian plane of the aperture. Expressions for the phase functions are derived. Computed results on the phase distribution and the radiation pattern are presented. View full abstract»

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  • Effect of jammer power on the performance of adaptive arrays

    Publication Year: 1984 , Page(s): 933 - 938
    Cited by:  Papers (11)
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    The effect of jammer power on the performance of adaptive arrays is studied. It is shown that the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array is a function of jammer power. In the presence of a wide-band jammer, the output SINR of the array decreases with an increase in jammer power and eventually goes to zero. Unlike continuous wave (CW) jammers, a wide-band jammer does not go through power inversion. Instead, as the jammer power is increased, the interference-to-noise ratio (INR) at the array output shows oscillations. For large jammer power, the output INR increases with an increase in jammer power. View full abstract»

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  • Frequency dependence of microwave depolarization versus rain attenuation

    Publication Year: 1984 , Page(s): 994 - 997
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    Calculations using oblate spheroidal raindrops, as well as measured data, demonstrated that rain-induced cross polarization amplitude is inversely proportional to frequency from 10 to 30 GHz. Except for extremely low rain rates ( \leq2.5 mm/h), the above frequency dependence has now been found to be true also for the more realistic (Pruppacher and Pitter shape) raindrops. Possible explanation for the misleading claim of inverse three-halves power frequency dependence was also explored. This clarification is presented to revise the frequency dependence of the International Radio Consultative Committee (CCIR) formula on rain-induced cross polarization versus attenuation. View full abstract»

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  • On the tunneling hypothesis for ray reflection and transmission at a concave dielectric boundary

    Publication Year: 1984 , Page(s): 978 - 986
    Cited by:  Papers (2)
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    When a ray field is incident on a concave boundary confining a dielectric medium, total reflection is perturbed by leakage due to surface curvature. The resulting modification of the conventional Fresnel ray reflection coefficient, including its uniform transition through critical incidence, has previously been addressed by the so-called "tunneling hypothesis," which is based essentially on the behavior of a corresponding peripherally guided whispering gallery or leaky modal field; the former exhibits evanescent decay (tunneling) away from the boundary in the exterior region but eventually gives rise to radiation from a caustic whereon the modal phase speed equals the speed of light. It is shown here that inferring local ray field properties from global mode field properties has limited validity. The demonstration is based on a rigorous analysis of the two-dimensional Green's function for a circular boundary. Asymptotic solutions are constructed for the various ray-optical domains, and for the transition regions near caustics and especially near the critically refracted ray. Examination of the reflected and transmitted fields reveals that the tunneling hypothesis holds only near the critically refracted ray. Elsewhere, the transmitted ray field may deviate markedly from that predicted by the tunneling model. The results clarify not only the ray field behavior but also the mechanism of local energy reflection and transmission for a nonplanar interface. View full abstract»

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  • Forward radiation from axially symmetric reflector antennas

    Publication Year: 1984 , Page(s): 893 - 901
    Cited by:  Papers (2)
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    The fields radiated from focus-fed symmetric reflector antennas in the vicinity of forward axial direction are determined by a series representation of the physical optics integral. The considered feeds have cosine-tapered patterns with different tapers in E - and H -planes. The influence of feed pattern asymmetry, subreflector blockage, feed taper, focal distance to diameter ( f/D ) ratio and the reflector size on the performance parameters of paraboloidal, Cassegrain, near-field Cassegrain, and corresponding Gregorian antennas is investigated. Design curves are presented to predict the performance parameters of the considered antennas. View full abstract»

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  • Probe-corrected spherical near-field antenna measurements

    Publication Year: 1984 , Page(s): 1012
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  • Propagation prediction for hilly terrain using GTD wedge diffraction

    Publication Year: 1984 , Page(s): 951 - 955
    Cited by:  Papers (48)  |  Patents (3)
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    A terrain sensitive propagation model based on the geometrical theory of diffraction (GTD) modified for finite conductivity and local surface roughness is applied to hilly terrain including multiple diffraction, with the results compared with measurements and the Longley-Rice model. Even though the approach used to calculate multiple-wedge diffraction is known to be invalid in certain situations, the comparison is favorable to the GTD model results. View full abstract»

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  • Sky brightness temperature measurements at 135 GHz and 215 GHz

    Publication Year: 1984 , Page(s): 928 - 933
    Cited by:  Papers (1)
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    Zenith sky brightness temperature measurements at 135 GHz and 215 GHz have been made on a semicontinuous basis for a period of seven months in the Gunston Cove area of Northern Virginia. These measurements were made using Dicke receivers with noise figures of 8 dB and 14 dB, respectively. A liquid nitrogen cooled load was used to calibrate the measurements. The 215 GHz sky temperature was on the average about 80 K greater than that at 135 GHz. Clouds were found to cause the sky temperatures to fluctuate as much as 150 K in a few minutes. Graphs are presented to outline general trends of the data as well as representative days, including the blizzard on February 11, 1983. In addition, empirical relations between precipitable water vapor, atmospheric water density at the surface, sky brightness temperatures, and zenith attenuation are given for visually clear days. View full abstract»

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  • Millimeter-wave beam steering using "Diffraction electronics"

    Publication Year: 1984 , Page(s): 987 - 990
    Cited by:  Papers (2)  |  Patents (5)
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    Periodic structures placed near a dielectric waveguide can cause the combined structure to radiate. The direction of radiation is controlled by the period or spacing of the elements in the structure. In the present study a simple coiled spring provided the periodic structure. Beam steering at 94 GHz over the range of 80\deg to 166\deg was achieved by flexing of the spring. The half-power beamwidth is determined by the total effective length of the structure at the radiated angle. The experimental results indicate that a relatively low-cost beam-steerable antenna for fan-type beams may be constructed. View full abstract»

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  • On variational electromagnetics: Theory and application

    Publication Year: 1984 , Page(s): 902 - 907
    Cited by:  Papers (20)
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    A methodology to he named variational electromagnetics (VEM) is introduced for handling time-harmonic linear electromagnetic field problems. First a desired variational formulation is derived from a fundamental variational principle (FVP) and then is solved by the hybrid element method along with the frontal solution algorithm. The main advantages of such an approach are the unified derivation of variational equations for both interior and exterior field problems and their efficient numerical solution, especially for problems with inhomogeneons media. Also included is a numerical example in which the scattering from an inhomogeneously coated cylinder is analyzed. View full abstract»

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  • High frequency fields in the presence of a curved dielectric interface

    Publication Year: 1984 , Page(s): 969 - 978
    Cited by:  Papers (4)
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    A high-frequency line source in a dielectric medium that is separated by a concave cylindrical boundary from an exterior medium with lower dielectric constant generates a variety of wave phenomena which have been explored extensively. This problem is reexamined here with a view toward clarifying relevant reflection and transmission characteristics within the framework of ray optics, with emphasis on the more complicated transmitted field. The exterior domain is divided into illuminated and shadow regions separated by the transmitted tangent ray launched by a ray incident at the critical angle. Conventional ray optics is valid far from the tangent ray shadow boundary on the illuminated side. The shadow boundary is surrounded by transition regions wherein Fock type integrals and Weber functions yielding local lateral waves provide alternative representations. On the shadow side, not too far from the shadow boundary, the field can be interpreted via "tunneling" and subsequent radiation along a ray from a virtual caustic to the observer. The tunneling is associated with the initial evanescent decay of the transmitted field excited by a totally reflected incident ray. However, deeper inside the shadow, this mechanism is inapplicable, and the field is expressed either in terms of the Fock integrals or a creeping wave-type residue series. The results are presented in a format that permits insertion into a geometrical theory of diffraction (GTD) user's manual. View full abstract»

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  • Microstrip antennas for dual-frequency operation

    Publication Year: 1984 , Page(s): 938 - 943
    Cited by:  Papers (37)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    Single element microstrip antenna for dual-frequency operation have been investigated. By placing shorting pins at appropriate locations in the patch, the ratio of two-band frequencies can be varied from 3 to 1.8. In many applications a smaller ratio is desired, and this can be achieved by introducing slots in the patch. In so doing, the ratio can be reduced to less than 1.3. For this type of antenna, a hybrid multiport theory is developed and theoretical results are found to be in excellent agreement with the measured. View full abstract»

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  • Susceptance computation of a meander-line polarizer layer

    Publication Year: 1984 , Page(s): 1007 - 1011
    Cited by:  Papers (7)
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    The solution to the problem of scattering of a plane wave by an infinite periodic array of meander-line thin conductors on a dielectric sheet is considered. Numerical results on perpendicular and parallel polarization susceptances are given as well as a comparison with experimental data over a large frequency range. Results showing variations of array's susceptances with respect to constitutive parameters are also presented. View full abstract»

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  • An adaptive array processor with robustness and broad-band capabilities

    Publication Year: 1984 , Page(s): 944 - 950
    Cited by:  Papers (35)  |  Patents (7)
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    A new type of receiving array which adaptively minimizes ouput noise power while simultaneously satisfying certain robustness and/or bandwidth criteria is considered. The resulting array gains are shown to be robust against direction uncertainty in the assumed look direction, against wavefront distortions and against array geometry errors. The robustness property is incorporated directly into the adaption algorithm via constraints. Extensive simulation has established very satisfactory performance of this new algorithm, both as a limited broad-band processor and as a robust narrow-band processor. View full abstract»

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  • Calculation of electrostatic fields surrounding finite circular cylindrical conductors

    Publication Year: 1984 , Page(s): 956 - 962
    Cited by:  Papers (1)
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    Analytical expressions are derived for the calculations of electric potentials and fields surrounding circular cylinders of finite lengths. Results of several examples are presented. View full abstract»

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  • The maximin algorithm for adaptive arrays and frequency-hopping communications

    Publication Year: 1984 , Page(s): 919 - 928
    Cited by:  Papers (28)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    An algorithm is described for maximizing of the signal-to-interference-plus-noise ratio (SINR) at the output of an adaptive array. The algorithm discriminates between the desired signal and any interference on the basis of the spectral characteristics of frequency-hopping signals. The algorithm maximizes the SINR by maximizing the desired.signal output power while simultaneously minimizing the interference-plus-noise output power. Rapid convergence of the weights to the steady-state values is achieved by the adjustment of the loop gain as a function of the estimated SINR at each iteration. Implementation of the algorithm in conjunction with a frequency-hopping modem is explained. Computer simulation results describe both the steady-state and transient responses of the system under various jamming conditions. The results indicate a rapid dynamic response and the steering of deep nulls over a wide range of the SINR. View full abstract»

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  • Circularly polarized conical patterns from circular microstrip antennas

    Publication Year: 1984 , Page(s): 991 - 994
    Cited by:  Papers (52)  |  Patents (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    A method is presented for generating circularly polarized conical patterns from circular microstrip antennas. These antennas are excited at higher order modes and require different feed arrangements for different mode excitations. It is determined that the peak direction of the conical pattern can be varied over a wide angular range. Modal expansion technique is employed to calculate the radiation patterns of these antennas. View full abstract»

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  • Radar cross section of a finite planar structure coated with a lossy dielectric

    Publication Year: 1984 , Page(s): 1003 - 1007
    Cited by:  Papers (3)
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    An asymptotic high frequency estimation of monostatic radar cross section (RCS) of a finite planar metallic structure coated with a lossy dielectric is made theoretically and compared with experiments in the X - band. An expression for RCS is obtained by using a diffraction coefficient involving Maliuzhinets' function. A closed form expression of the Maliuzhinets' function has been developed. Corner diffraction effects are not considered. A continuous wave (CW) monostatic RCS measurement set up has been used to verify the theoretical results experimentally. A typical reduction with a single coating of epoxy resin of thickness equal to \lambda /20 is of the order of 5 dB for normal incidence compared to a conducting plate of the same size. 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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Editor-in-Chief                                                 Kwok W. Leung