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Antennas and Propagation, IEEE Transactions on

Issue 6 • Date June 2002

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Displaying Results 1 - 19 of 19
  • Radial field retrieval in spherical scanning for current reconstruction and NF-FF transformation

    Page(s): 866 - 874
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (386 KB) |  | HTML iconHTML  

    A near-field to far-field (NF-FF) transformation is addressed for the case of spherical scanning using equivalent magnetic currents (EMCs) and matrix methods. It is based on the decoupling of the field components and the iterative retrieval of the radial component of the electric field. The technique is applied for far-field calculation as well as for the estimation of the current distribution of the antenna under test (AUT) using spherical near-field facilities. Results from measured near-field data of several antennas are presented and compared to those of the analytical solution via a spherical wave mode expansion method. View full abstract»

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  • On the size requirement for finite phased-array models

    Page(s): 836 - 840
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (269 KB) |  | HTML iconHTML  

    The question considered is how large an array model must be in order to capture approximately the characteristics of both the interior and the edge elements of a large multi-octave phased array. Arrays with tapered slot elements and with top-loaded dipoles are analyzed at element spacings as small as 0.1λ and it is concluded that at any frequency, a finite array model with this type of element should be at least 5λ×5λ in size. This suggests the generalization of the 10×10 element model often used as an engineering "rule of thumb" in the normal narrow-band case with 0.5λ element spacing. An array model with a 5:1 bandwidth thus needs about 25 times more elements than a narrow-band model. The array feed impedance is considered and it is found that the array active reflection coefficient in finite arrays but not in infinite arrays is dependent on the matching condition at the feed. The finite-difference time-domain (FDTD) technique is used to analyze arrays up to 49×49 elements, demonstrating that computer power now makes feasible the full wave solution for large phased arrays with complex geometry View full abstract»

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  • Pattern characteristics of harmonic and intermodulation products in broadband active transmit arrays

    Page(s): 858 - 865
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (299 KB)  

    A three-term power series model for the nonlinearity in the power amplifiers of an active array is used to explore the radiation characteristics of the harmonics and intermodulation products. This model leads to simple equations for predicting the beam-pointing direction and the aperture amplitude taper of the spurious signals. Cases of a single transmit signal, dual transmit signals within a single beam and dual beam operations are analyzed. This model shows that the second and third harmonics are co-boresighted with the fundamental signal but have squared and cubed aperture amplitude distributions. The third-order intermodulation products in general have beam-pointing directions offset from the fundamental signal beam(s). Graphical methods of locating the intermodulation beams in (u, v) space are outlined and illustrated by example View full abstract»

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  • Analysis of elliptical microstrip patch antenna considering attachment mode

    Page(s): 888 - 890
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (247 KB) |  | HTML iconHTML  

    This paper presents an analysis of an elliptical microstrip patch antenna for circular polarization using the method of moments (MOM) in conjunction with the reaction integration method. The attachment mode was used to ensure the continuity and the singularity of the currents in the patch-probe conjunction point. Results showed that an elliptical patch can be used to generate circular polarization with one probe feed and attachment mode should be used to obtain the exact impedance when excited by a probe View full abstract»

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  • Planar double-layer leaky-wave microstrip antenna

    Page(s): 832 - 835
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB) |  | HTML iconHTML  

    This paper presents a double-layer leaky-wave microstrip antenna that is entirely planar for easy fabrication. The cavity model and the full-wave spectral domain method are used to analyze the proposed structure. The results from these two approaches agree well with experimental data. The planar structure makes the leaky-wave antenna convenient for implementation in a monolithic microwave integrated circuit (MMIC) environment. Also, due to the flexibility of the microstrip structure, the geometrical shape can be modified for other desirable radiation patterns View full abstract»

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  • An efficient algorithm for solving Zakharov-Shabat inverse scattering problem

    Page(s): 807 - 811
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (249 KB)  

    An efficient numerical method for solving Zakharov-Shabat (ZS) inverse scattering problem is presented. In this method, instead of equivalent second-order differential equations to the Gel'fand-Levitan-Marchenko (GLM)-type integral equations, equivalent first-order differential equations are adopted and sufficiently accurate solutions to Zakharov-Shabat inverse problem can be achieved without iterations. Examples for applying it to design nonuniform transmission line (NTL) filters are also provided View full abstract»

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  • Generalization of the equivalence between physical optics and aperture integration for radiation from open-ended structures

    Page(s): 891 - 893
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (203 KB)  

    The theorem of equivalence between the Kirchhoff aperture integration (AI) and the physical optics (PO) approach applied to the interior walls of a open-ended waveguide is generalized to the case of any open-ended structure (OES) View full abstract»

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  • Application of Haar-wavelet-based multiresolution time-domain schemes to electromagnetic scattering problems

    Page(s): 774 - 784
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (466 KB) |  | HTML iconHTML  

    The multiresolution time-domain (MRTD) algorithm is applied to the problem of general two-dimensional electromagnetic scattering. A Haar wavelet expansion is utilized. A parallel between Haar MRTD and the classic Yee finite-difference time-domain (FDTD) algorithm is discussed, and results of simulations on canonical targets are shown for comparison. We focus on the incident-field implementation, which, in our case, consists of a pulsed plane wave. Also, we consider scattering in a half-space environment, with application to subsurface sensing. The results illustrate the advantage of the Haar MRTD method as compared with the classic FDTD, which consists of reduced memory and execution time requirements, without sacrificing accuracy View full abstract»

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  • Broadband probe-fed patch antenna with a W-shaped ground plane

    Page(s): 827 - 831
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    A new design of a broadband probe-fed patch antenna with a W-shaped ground plane is presented. The W-shaped ground plane is obtained by bending the conventional planar ground plane into an inverted V-shape, seen in the resonant direction of the patch antenna and then adding proper flanges at the two straight edges of the bent ground plane. The proposed design is applicable to the patch antenna with a planar radiating patch with a thin air substrate. With the use of the proposed W-shaped ground plane, the required probe-pin length in the substrate remains small, although the effective substrate thickness is significantly increased, resulting in a much wider operating bandwidth. Also, by choosing proper dimensions of the W-shaped ground plane, the antenna gain for frequencies over the obtained wide bandwidth is enhanced, compared to the conventional patch antenna with a planar ground plane. In addition, the cross polarization is also reduced for the proposed design and the cross-polarization level (XPL) in the H-plane pattern can even be better than that of a conventional probe-fed patch antenna with a thin air substrate View full abstract»

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  • Modified constant modulus algorithm for digital signal processing adaptive antennas with microwave analog beamforming

    Page(s): 850 - 857
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (302 KB)  

    This paper proposes a novel algorithm, called modified constant modulus algorithm (M-CMA), which is able to give adaptability to microwave beamforming phased array antennas. Since microwave analog beamformers basically require much fewer RF devices than digital beamformers, microwave analog beamformers based on M-CMA, that is, adaptive microwave beamformers, can be cheaply fabricated. Therefore, they are very suitable for mobile communication systems where both miniaturization and low cost are required for the mobile terminals. M-CMA obtains a gradient vector by a combination of analytical calculation and perturbation of the microwave beamforming control voltage. Though M-CMA is implemented with a digital signal processor, M-CMA controls the microwave analog beamformer by utilizing the gradient vector. The microwave analog beamformer based on M-CMA is analyzed to have the following characteristics: (1) the beamformer can point its main beam to the desired direction in additive white Gaussian noise (AWGN) channels; (2) although the beamformer may possibly fail in ill solutions in cochannel interference (CCI) channels, M-CMA can converge to the optimum solution when the desired direction is roughly a priori known View full abstract»

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  • Investigations into a power-combining structure using a reflectarray of dual-feed aperture-coupled microstrip patch antennas

    Page(s): 841 - 849
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    This paper details an investigation of a power combiner that uses a reflectarray of dual-feed aperture-coupled microstrip patch antennas and a corporate-fed dual-polarized array as a signal distributing/combining device. In this configuration, elements of the reflectarray receive a linearly polarized wave and retransmit it with an orthogonal polarization using variable-length sections of microstrip lines connecting receive and transmit ports. By applying appropriate lengths of these delay lines, the array focuses the transmitted wave onto the feed array. The operation of the combiner is investigated for a small-size circular reflectarray for the cases of -3 dB, -6 dB and -10 dB edge illumination by the 2×2-element dual-polarized array View full abstract»

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  • Spectral acceleration of the generalized forward-backward method

    Page(s): 785 - 797
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (465 KB)  

    The generalized forward-backward (GFB) method was introduced as an iterative method of moments solution to compute the electromagnetic scattering from targets on ocean-like rough surfaces. In this paper, an existing spectral acceleration algorithm is adapted to the GFB. The spectral acceleration is presented for both polarizations and for perfect electrically conducting (PEC) and non-PEC surfaces. The accelerated scheme reduces the computational scaling cost of the GFB from O(N2) to O(N) per iteration as the length of the sea surface increases linearly with the number of unknowns N. The numerical results demonstrate that the spectral acceleration introduces negligible error while greatly improving the efficiency of the GFB method View full abstract»

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  • Time-domain imaging of objects within enclosures

    Page(s): 895 - 898
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB)  

    The imaging of objects within an enclosure using short electromagnetic pulses is investigated. A simulated image of a metallic cylinder within a plywood box is constructed using the numerical scattered field found by solving an integral equation. Comparison with images found experimentally shows good agreement, and the object is easily detected through the walls of the box. Multiple objects placed within the plywood box are imaged with similar clarity View full abstract»

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  • Design and scan performance of large, probe-fed stacked microstrip patch arrays

    Page(s): 893 - 895
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (289 KB)  

    A strategy is presented on how to design large, direct-contact microstrip patch arrays with broad bandwidths and useful scanning ranges. It is shown that to maximize these characteristics the lower layer of a stacked patch configuration must have a relatively high dielectric constant, greater than 10 and the upper laminate must have a low dielectric constant value. Doing so yields bandwidths in excess of 25% over a scanning range of ±45° in the principle planes. Such arrays may be suitable for millimeter-wave systems such as collision avoidance radars and microcellular mobile communication base stations View full abstract»

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  • An estimate of the error caused by the plane-wave approximation in free-space dielectric measurement systems

    Page(s): 878 - 887
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    In a free-space measurement system, the electrical constitutive parameters of a plane sheet of material are determined using incident, transmitted and reflected electromagnetic beams. The electrical parameters are almost always obtained from the measured transmission and reflection coefficients using a procedure that approximates each beam as a single plane wave whose wavefront is parallel to the surfaces of the sheet (the plane-wave approximation). A theoretical model is constructed to investigate, in a very general way, the limitations of the plane-wave approximation. The field of the incident beam is taken to be a Gaussian function at the center of the sheet and analytic expressions are obtained for the transmitted and reflected beams using the plane-wave spectrum technique. Power transmission and reflection coefficients are calculated and series expansions of these coefficients are used to determine under what conditions the plane-wave approximation applies. Graphical results are presented to show how the error associated with the plane-wave approximation depends on the various parameters for the problem: electrical size of the beam waist, electrical thickness of the sheet etc View full abstract»

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  • Scattering from periodic array of grounded parallel strips, TE incidence

    Page(s): 798 - 806
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    The field distribution between strips in a periodic array of parallel strips was modeled. The electric field integral equation (EFIE) together with method of moments (MoM) was employed to solve the problem. The incident plane wave was assumed to be transverse electric (TE). The effect of the incident angle on the field between strips was investigated. For comparison, an array of the same configuration but containing a finite number of parallel strips was also modeled using the EFIE and solved via MoM. Good agreement was found even when the number of strips was small. The results are of interest for mobile radio View full abstract»

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  • Experimental verification of the generalized Schelkunoff's horn-gain formulas for sectoral horns

    Page(s): 875 - 877
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    An approximate formula has been recently proposed for the on-axis gain of rectangular waveguide antennas, that include open-ended rectangular waveguides and sectoral and pyramidal horns (see Selvan, K.T., IEEE Trans. Antennas Propagat., vol.47, p.1001-4, 1999). This formula is an approximate generalization of S.A. Schelkunoff's horn-gain formulas (see "Electromagnetic Waves", Van Nostrand, p.360-4, 1943). Gain measurements are reported for the gains of E plane and H plane sectoral horns and are used in an examination of the accuracy of Selvan's formulas. To the best of the authors' knowledge, these are the first ever measurement efforts on the gain of H-plane sectoral horns View full abstract»

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  • Modeling of normal-mode helical antennas at 900 MHz and 1.8 GHz for mobile communications handsets using the FDTD technique

    Page(s): 812 - 820
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (449 KB) |  | HTML iconHTML  

    A simple technique is proposed for modeling short normal-mode helical antennas using a commercial finite-difference time-domain (FDTD) code with a rectangular grid and a nominal extension of the wire. The approach allows affects on the input impedance and radiation performance of the helix to be examined and importantly does not require modification of the excitation subroutines. Normal-mode helical antennas for mobile communications use at 900 and 1800 MHz were designed using the proposed method and good agreement with measurements of impedance and near-magnetic field strength was found. The radiating performance of the helix was compared to that of a λ/4 monopole and generally found to be inferior at 900 MHz due to only 19.2 % efficiency in the presence of the head. At 1.8 GHz the two antenna types showed similar characteristics except in regard to bandwidth, 36.1 % for the monopole and 7.8 % for the helix, in the presence of the head. The modeled helix antennas produce spatial peak specific absorption rate (SAR) figures that are up to 27 % greater at 900 MHz and up to 49 % greater at 1.8 GHz than the corresponding monopole values due to the shorter antenna View full abstract»

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  • Dependence of the efficiency-bandwidth product on electrical volume of small dielectric loaded antennas

    Page(s): 821 - 826
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (249 KB) |  | HTML iconHTML  

    The efficiency fractional efficiency bandwidth product (EB) that is expressed as a ratio of the radiation resistance to the absolute value of an input reactance of an antenna is used as a performance measure for small dielectric-loaded monopole antennas (DLMAs). The dependence of the efficiency bandwidth (EB) on the permittivity of the dielectric loading (i.e., the electrical volume) is experimentally investigated for the first time after we succeeded in measuring the small radiation resistance of the DLMAs precisely on the basis of the Wheeler cap method. As a result, it was found that the EBs of some DLMAs were enhanced over a bare monopole antenna and an EB characteristic curve has a maximum point. This result suggests the presence of the optimum electrical volume for the dielectric loading in order to obtain the best EB performance. A calculation by the finite-difference time-domain (FDTD) method was also conducted to confirm the presence of the maximum EB value under a certain condition. A general reason for the existence of the peak value is also explained using a mathematical deduction 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