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Antennas and Propagation, IEEE Transactions on

Issue 11 • Date Nov 1990

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Displaying Results 1 - 25 of 28
  • Constrained least squares in adaptive, imperfect arrays

    Page(s): 1874 - 1878
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    Two new constrained deterministic least-squares algorithms are presented which are capable of enabling a narrow-band zero-order generalized sidelobe canceller (SLC), in the presence of array imperfections, to null out jammers while preserving the friendly look-direction signal with minimal a priori knowledge of the signal environment. The algorithms are capable of solving deterministic least-squares optimization problems subject to an equality constraint in an iterative, adaptive manner by imposing a `soft' constraint via the quadratic penalty function optimization method. The first algorithm is based on the matrix inversion lemma while the second is obtained by means of QR-decomposition using new three-dimensional Givens (1958) rotations and implemented with a systolic array architecture. These new constrained algorithms improve system performance when an artificial injection of a receiver noise vector is introduced View full abstract»

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  • An antenna pattern measurement technique for eliminating the fields scattered from the edges of a finite ground plane

    Page(s): 1815 - 1822
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    A novel antenna pattern measurement technique is presented to eliminate the effects of the finite ground plane and anechoic chamber wall reflections which significantly perturb antenna pattern measurements. This technique consists of the measurement of the edge-diffracted fields and their subsequent subtraction from the original pattern. A simple theoretical model is developed to introduce the subtraction technique, and comparisons are made which show the excellent agreement between theoretical (assuming an infinite ground plane) and `corrected' experimental antenna patterns. Experimental results are given for open-ended waveguide, microstrip patch, and monopole antennas mounted on circular and square ground planes of various sizes. Time gating techniques are illustrated as well View full abstract»

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  • Pulsed beam reflection and transmission at a dielectric interface: two-dimensional fields

    Page(s): 1791 - 1800
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    Highly focused pulsed fields in vacuum can be generated analytically by assigning complex values to the space-time source coordinates of the conventional transient free-space Green's function. These new wave objects have been named complex-source pulsed beams (CSPB). Their utility can be extended to generating new solutions for pulsed beam propagation and diffraction in a perturbed environment by making the space-time source coordinates in the corresponding Green's function complex. The analytic extension required in this process is performed systematically via the spectral theory of transients. A canonical test case for reflection, including critical angle, lateral (head) wave and evanescent transmission effects, is provided by a dielectric half-space. The exact solution for CSPB scattering is derived in spectral integral form, evaluated in terms of the time-dependent spatial spectrum singularities in the complex plane, and interpreted physically. Numerical evaluation reveals the detailed space-time behavior of these physical constituents and their role in establishing the total scattered field. To simplify the analysis, a two-dimensional problem is considered wherein the pulsed beam is generated by a complex pulsed line source View full abstract»

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  • A wide-band prime-focus horn for low-noise receiver applications

    Page(s): 1898 - 1900
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    A horn suitable for a prime-focus antenna requiring low cross polarization, wide bandwidth, and low spillover is described. The design is particularly suited for low-noise applications such as high-quality satellite earth-station antennas and radio telescopes. The horn has a return loss substantially better than 20 dB, a cross polar sidelobe level better than -20 dB, a beamwidth variation of 40% and negligible phase center shift View full abstract»

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  • Current induced by TE excitation on coupled and partially buried cylinders at the interface between two media

    Page(s): 1823 - 1828
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    An analysis is described for determining the current induced by transverse electric (TE) excitation on coupled conducting cylinders near the planar interface separating two semi-infinite homogeneous half-spaces of different electromagnetic properties and on partially buried conducting cylinders. The conducting cylinders, of general cross section, are of infinite extent and the excitation is transverse electric to the cylinder axes. Coupled integral equations for the currents induced on the cylinders are formulated and numerical methods for solving them are presented. Data showing the induced current distribution for various cylinders and media parameters of interest are presented and discussed. Relative to the homogeneous space case, the presence of the two media significantly alters the current distribution, especially near the interface View full abstract»

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  • The performance of the SMI method in the constrained LMS array and the Griffiths array

    Page(s): 1878 - 1882
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    The sample matrix inversion (SMI) method is applied in the constrained least mean square (LMS) array of the Griffiths (1959) array. The mean square error (MSE) performance measure of the SMI method in both arrays is presented. The total output power (TOP) performance of the SMI method in the constrained LMS array is also presented. In using the SMI method to obtain the MSE and the TOP of the constrained LMS array, the adaptive weight vector is computed based on the estimate of the received signal correlation matrix and the knowledge of the arrival angle of the desired signal. The weight vector of the Griffiths array is also computed, based on the estimate of the correlation matrix and the knowledge of the cross correlation vector between the reference signal and the received signal View full abstract»

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  • Electromagnetic field analysis of a four-wire anechoic chamber

    Page(s): 1835 - 1842
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    The electromagnetic field characteristics and plane-wave generating ability of a parallel four-wire anechoic chamber which is to be operated in the VHF range is analyzed. The analysis considers three cases: the first is a four-wire chamber when only a thin layer of absorber material covers the chamber walls, the second is a four-wire chamber when only free space surrounds the four wires of the system, and the third is a four-wire chamber when a thick layer of absorber material covers the anechoic chamber walls. The three cases are analyzed by a variety of mathematical methods including the method of moments, waveguide theory, and a finite-difference time-domain method. Numerical results for the propagation constants and electromagnetic fields that are generated in the chamber in the three cases are presented View full abstract»

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  • Diffraction by a plane angular sector, a new derivation

    Page(s): 1892 - 1894
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    An alternative derivation is given for the exact solution to the scattering problem in which a Hertz dipole illuminates a perfectly conducting plane angular sector. Specifically, the Ohm-Rayleigh method is used rather than that of Satterwhite (1969) View full abstract»

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  • TE scattering by partially buried and coupled cylinders at the interface between two media

    Page(s): 1829 - 1834
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    The scattering of transverse electric (TE) illumination by partially buried conducting cylinders and by coupled conducting cylinders in two media is studied. The conducting cylinders are of general cross section and of infinite extent. Data depicting far-zone scattered fields for various cylinders and media parameters of interest are presented, and the highly lobate patterns which differ significantly from those due to cylinders in homogeneous space are discussed and explained View full abstract»

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  • A combined finite element-boundary integral formulation for solution of two-dimensional scattering problems via CGFFT

    Page(s): 1852 - 1858
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    A novel technique is presented for computing the scattering by two-dimensional structures of arbitrary inhomogeneity. The proposed approach combines the usual finite-element (FE) method with the boundary-integral equation to formulate a discrete system. This is subsequently solved via the conjugate gradient (CG) algorithm. A particular characteristic of the method is the use of rectangular boundaries to enclose the scatterer. Several of the resulting boundary integrals are then convolutions and can be evaluated via the fast Fourier transform (FFT) in the implementation of the CG algorithm. The solution approach presented here offers the principal advantage of having O(N) memory demand and employs a one-dimensional FFT, as against the two-dimensional FFT required in a traditional implementation of the proposed CG-FFT algorithm. The speed of the proposed solution method is compared with that of the traditional CG-FFT algorithm. Results are presented for several rectangular composite cylinders and one perfectly conducting cylinder. These are shown to be in excellent agreement with the moment method View full abstract»

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  • Evaporation duct effects on sea clutter

    Page(s): 1765 - 1771
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    Existing sea clutter models are in general agreement on the trends and magnitudes of sea reflectivity at low (1°-10°) grazing angles. However, at extremely low grazing angles (<1°), models, theory, and measurements show considerable differences. The effects of the oceanic evaporation duct on grazing angle are investigated. Significant changes in grazing angle due to the evaporation duct are found and the illumination of the sea surface by the radar is shown to extend well beyond the standard (4/3 earth) radar horizon range. A series of sea clutter model comparisons shows that much of the difference between models can be attributed to evaporation duct effects View full abstract»

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  • An inherent limitation of the Luneburg-Kline representation for the current on a conducting body

    Page(s): 1889 - 1892
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    An attempt is made to determine fundamental limitations, e.g. limitations not imposed by an inability to perform integrals, of a Luneburg-Kline (L-K) representation for the surface current induced on a conducting surface by a plane wave. By expanding the current, normalized by the incident field phase factor, in an L-K series and substituting this result in the magnetic-field integral equation, it is found that all the coefficients in the expansion are identically zero in the shadow region of the scatterer. This limitation is explained in terms of the inability of the L-K series to adequately represent the creeping-wave nature of the current in the transition/shadow region. These results raise the question of the physical source of previously derived higher-order L-K terms View full abstract»

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  • An efficient plane wave spectral analysis to predict the focal region fields of parabolic reflector antennas for small and wide angle scanning

    Page(s): 1746 - 1756
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    An efficient approach is described for calculating the field distribution in the focal region of an electrically large, symmetric or offset parabolic reflector antenna with an arbitrary rim contour, when the concave reflector surface is fully illuminated by an obliquely incident arbitrary electromagnetic plane wave. The dominant contribution to the focal-region fields is found by transforming the physical-optics integral over the reflector surface into a plane-wave spectral (PWS) integral. The PWS integral is evaluated rapidly via the fast Fourier transform (FET) algorithm to furnish, in only a single computation, the field for every place in the focal plane (or any plane parallel to it) within the focal region for a given direction of the incident wave. The correction to the physical-optics field is relatively small in the focal region and may therefore be neglected. Numerical results based on this PWS approach are presented, and their accuracy is established by comparison with results based on other approaches View full abstract»

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  • On the design of nonuniformly spaced slot arrays

    Page(s): 1780 - 1783
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    A technique for the design of nonuniformly spaced waveguide slot arrays is proposed. The slots are in active resonance, and their position is adjusted so that the sources of the array will have the desired amplitudes and phases. The conductances of the slots depend on the desired pattern and the efficiency. Applications on Taylor and cosec 2θ patterns have shown the validity of the method View full abstract»

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  • The electromagnetic field of a slotted elliptic cone

    Page(s): 1894 - 1898
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    The exact solution for the electromagnetic field diffracted by a perfectly conducting slotted elliptic cone is determined. The solution is presented in the form of a dyadic Green's function, which is the most general form of a possible solution. Some numerical results are presented and compared with others given in the past for simpler geometries View full abstract»

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  • Electromagnetic scattering from and transmission through arbitrary apertures in conducting bodies

    Page(s): 1805 - 1814
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    The general 3-D aperture coupling problem is formulated in terms of an integral equation for the equivalent magnetic current in the aperture, which is numerically solved by the method of moments. The aperture is characterized by two aperture admittance matrices, one for the exterior region and the other for the interior region. These two admittance matrices are determined separately but in a similar manner if the pseudo-image method is used. Numerically workable expressions are developed for the two aperture admittance matrices by decomposing each of them into a half-space admittance matrix and a supplementary admittance matrix. The half-space admittance is relatively easy to compute and has been investigated in the literature. The supplementary admittance matrix is expressed in terms of the generalized impedance combining the existing numerical codes for an arbitrarily shaped scatterer and for an arbitrary aperture in a conducting plane, one can obtain a code which is especially designed for an arbitrary aperture in a conducting surface of arbitrary shape View full abstract»

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  • Analysis of untilted edge slots excited by tilted wires

    Page(s): 1737 - 1745
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    An untilted narrow wall slot, cut between a pair of tilted strips inside a rectangular waveguide, has been analyzed. The combination is excited internally by a TE10 mode and the slot radiates externally. This slot/tilted-strips element behaves like a shunt admittance on an equivalent transmission line. This feature can be utilized to design arrays of such slots. Coupled integral equations are derived and solved, using the method of moments, to obtain the slot aperture E-field and the internal forward and backward scattering. Numerical and experimental results are presented to validate the method and to discover the range of useful dimensions for this composite element View full abstract»

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  • Traveling wave lobe locations

    Page(s): 1859 - 1862
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    A simple and reasonably accurate formula for the angular locations of traveling wave lobes has been available for many years, but the formula holds only for surface waves that travel at the speed of light. It is shown how the formula may be modified to account for propagation velocities less than the speed of light. It is shown that when the equation derived by the author is used to estimate a starting value for cosQ in the Newton-Raphson method, the solution usually requires no more than three iterations for an accuracy of 10-6 in the solution for Q View full abstract»

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  • The effects of an ionospherically induced partially coherent wavefront on the performance of a thinned random antenna array

    Page(s): 1801 - 1804
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    Very large aperture antenna arrays are being planned for future military applications. It is known that due to irregularities in the ionosphere, where the reflection process takes place, the wavefront across such apertures becomes less coherent as the aperture size is increased. The main thrust of this study is to examine the degradation in the antenna gain and pattern characteristics of a thinned linear array, with 100 elements randomly spaced with a Hamming spatial taper, over a baseline of 10 km, for frequencies from 6 to 30 MHz. These results are then compared with those for a filled linear array having 400 Hamming amplitude-weighted elements and a baseline of 10 km. It is found that the effects of a partially coherent wavefront on the thinned array are comparable to those for the filled array in that the loss in gain and main-beam broadening are similar View full abstract»

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  • A Taylor synthesis for principal solution patterns of multiplicative antenna systems

    Page(s): 1848 - 1851
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    A multiplicative (cross-correlation) receiving antenna system with a linear aperture can have a power pattern P0(u ) (the so-called principal-solution power pattern) whose spatial frequency transfer function (SFTF) is uniform over the entire spatial frequency (SF) bandwidth. A modified principal solution system which retains the uniform SFTF except for smooth transitions at the ends of the SF passband is described. The transitions are due to a change in the original pattern P0(u), which suffers from high sidelobes, to a Taylor (1955) synthesis pattern PT (u) which involves a slowly varying envelope pattern. All of the slowly varying envelope sidelobes of PT(u ) are set at the same appropriate low level, e.g. -30 dB. The aperture weighting distributions are free of singularities, unlike those for P0(u), and can be sampled to provide the current weightings for a linear multiplicative array View full abstract»

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  • Far-field pattern determination from the near-field amplitude on two surfaces

    Page(s): 1772 - 1779
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    The possibility of determining the far field of radiating systems by measuring only the near-field amplitude is investigated. The main difficulties of the problem are examined in some detail and a new near-field/far-field transformation technique is developed, based on the measurement of the near-field amplitude over two surfaces surrounding the antenna under test. The accuracy of the far-field reconstruction results are related both to the distance between such surfaces and to some a priori information concerning the near-field phase and/or the radiating system. The information on the radiating system allows relaxation of the need for any information on the near-field phase provided that the distance between the measurement surfaces is high enough. Conversely, the knowledge of a more or less corrupted near-field phase allows reduction of such distances without affecting the accuracy of the far-field reconstruction. Numerical examples validating the effectiveness of the developed algorithm are provided for the planar scanning case View full abstract»

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  • A new model for calculating the input impedance of coax-fed circular microstrip antennas with and without air gaps

    Page(s): 1882 - 1885
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    A model is presented for calculating the input impedance of a probe-fed circular antenna with and without air gaps between the substrate and the ground plane. It is based on the cavity method, the dynamic permittivity constant (to take into account the influence of the fringing field at the edge of radiating element), and the resonant parallel R-L-C circuit with an inductive reactance. Numerical results are shown to agree well with experimental ones. The model is well suited for computer-aided design View full abstract»

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  • Time domain version of the uniform GTD

    Page(s): 1757 - 1764
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    The uniform geometrical theory of diffraction (UTD) solutions can be inversely transformed analytically to obtain a time-domain version of the UTD. The time-domain solutions are valid in the early time period where an observation time t is close to the time after the arrival of the first diffracted wavefront. Comparisons with GTD (geometrical theory of diffraction) and also with available rigorous results (J.B. Keller and A. Blank, 1951) reveal that the UTD solutions are accurate for substantial early time periods while the GTD (Keller and Blank) results are valid for very early time periods View full abstract»

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  • Target discrimination using multiple-frequency amplitude returns

    Page(s): 1885 - 1889
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    A technique for radar target discrimination using multiple-frequency scattering amplitude data is investigated. Based on the concept of natural resonance frequencies, the technique is aspect-angle independent. This is achieved through simple signal processing, thus providing nearly real-time operation. The radar cross sections (RCS) of spheroids are calculated numerically to simulate the received radar returns for discriminating different spheroids and wires in the resonance frequency region. The simulation also takes into account the effect of noise which appears in practical measurement View full abstract»

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  • Input admittance of a biconical antenna with wide feed gap

    Page(s): 1784 - 1790
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    The biconical antenna fed across a wide feed gap is studied as a boundary-value problem, using modal analysis. The study deals with finite-length antennas. It also includes the consideration of two limiting cases of biconical antennas, i.e. wide angle (spherical antennas) and very small angle (thin wire antennas). Expressions for the input as well as apparent terminal admittances are derived and corresponding values compared with available literature data for vanishingly small feed gap widths (delta function generator) 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