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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date Jul 1997

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Displaying Results 1 - 17 of 17
  • Three-dimensional edge-based finite-element analysis for discrete bodies of revolution

    Publication Year: 1997 , Page(s): 1160 - 1165
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    An extension to three-dimensional (3-D) edge-based finite-element analysis for modeling electrically large fan-like bodies as discrete bodies of revolution is given. By exploiting the overlapping symmetries between a fan-like body and a modal expansion of the electromagnetic fields, only one lobe of the problem need be solved by the finite-element method without introducing approximations. This computational scaling makes possible the solution of electrically large structures much more efficiently. However, a periodic phase-boundary condition (PBC) must be applied to the faces of the mesh describing a single slice of the body and this condition must be enforced on both the electric and magnetic fields for a robust solution. Details on the implementation of the PBCs are given along with results which validate the overall technique View full abstract»

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  • Analysis and characterization of ultrawideband scalar volume sources and the fields they radiate

    Publication Year: 1997 , Page(s): 1098 - 1106
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    This paper investigates a certain class of three-dimensional (3-D) (volume) sources to the scalar wave equation that are capable of radiating high-amplitude short-duration pulses in a selected (main) direction and low-amplitude long-duration pulses in other directions. Parameterization and characterization of such sources and the fields that they radiate is carried out in both the frequency and time domains and various measures of ultrawideband radiation (transmit mode) performance are evaluated and discussed within both domains. Frequency and time-domain results corresponding to uniformly distributed parallelepiped sources are presented to elucidate the role of the source's space distribution on the radiation performance. These results provide insight about the possibility of optimizing the radiation performance of scalar, ultrawideband volume sources by a proper selection of the space distribution of the source View full abstract»

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  • Circular polarization microstrip antenna on a conical surface

    Publication Year: 1997 , Page(s): 1086 - 1092
    Cited by:  Papers (6)
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    A theoretical model to analyze the performance of a circular polarization microstrip antenna printed on a conical surface is presented. The radiation pattern of the antenna is simulated by the radiation from its four radiating edges (two axial and two circumferential). The electromagnetic field is expanded in terms of spherical wave modes and it is shown that the circular polarization is obtained by exciting in the antenna two spherical TEr orthogonal modes with 90° phase difference. The impedance analysis is based on the cavity model. Experimental data fits well the theoretical predictions of the model View full abstract»

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  • Sidelobe reduction in array-pattern synthesis using genetic algorithm

    Publication Year: 1997 , Page(s): 1117 - 1122
    Cited by:  Papers (154)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    A simple and flexible genetic algorithm (GA) for pattern synthesis of antenna array with arbitrary geometric configuration is presented. Unlike conventional GA using binary coding and binary crossover, this approach directly represents the array excitation weighting vectors as complex number chromosomes and uses decimal linear crossover without a crossover site. Compared with conventional GAs, this approach has a few advantages: giving a clearer and simpler representation of the problem, simplifying chromosome construction, and totally avoiding binary encoding and decoding so as to simplify software programming and to reduce CPU time. This method also allows us to impose constraints on phases and magnitudes of complex excitation coefficients for preferable implementation in practice using digital phase shifters and digital attenuators. Successful applications show that the approach can be used as a general tool for pattern synthesis of arbitrary arrays View full abstract»

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  • UTD multiple-edge transition zone diffraction

    Publication Year: 1997 , Page(s): 1093 - 1097
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    The uniform theory of diffraction (UTD) is applied to multiple absorbing screens, which are in the transition zones near shadow boundaries. The theory includes the application of slope diffraction, which is a first-order effect in transition zone diffraction. By choosing length parameters independently for amplitude and slope diffraction, it is ensured that the solution has continuity of amplitude and slope at each point. The solution is compared with known solutions with good results except when two screens are very near each other. The study is of particular interest to radio propagation over terrain in mobile radio systems View full abstract»

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  • Calibration and measurement of a wideband six-port polarimetric measurement system

    Publication Year: 1997 , Page(s): 1080 - 1085
    Cited by:  Papers (2)
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    The principle of operation, calibration procedure, and experimental results of a wideband six-port polarimetric measurement system are described in this paper. This measurement system can measure the polarization states of incoming waves and the polarimetric scattering matrices of scattering targets from the wideband power data. The imbalances and coupling between antenna polarization channels and the characteristics of microwave components used in the measurement system are calibrated using three partly unknown scattering calibrators that are illuminated by four unknown-polarized calibrating waves View full abstract»

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  • Antenna characterization in the time domain

    Publication Year: 1997 , Page(s): 1140 - 1149
    Cited by:  Papers (121)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    A theory for a complete far-field transmit-receive system characterization of short-pulse antennas is derived in the time domain. The transmit-receive antenna system is characterized by a set of cascaded operators, which transform the source waveform and power into similar quantities at the receiving antenna terminals. Two such sets are defined. The first one is phrased in terms of the wave-type “time-dependent effective-height” operator, while the second one is defined in terms of the energy-type “gain operator”. Both definitions fit within a complete transmit-receive system description, the latter being equivalent to the frequency-domain Friis equation. However, these operators are derived entirely in the context of the time-domain field equation. The starting point in the time-domain analysis of the effective height is the slant stack transform (SST) of the time-dependent current distribution in a manner equivalent to the spatial Fourier transform used in the frequency domain. The vector autocorrelation of the transmitting effective height is then used to define the time-dependent gain operator under impulsive source excitation. Time-domain reciprocity leads to the definitions of antenna parameters under receiving conditions and the corresponding equivalent circuit. The parameters defined in this way fit within a consistent transmit-receive convolution operator, operating on the autocorrelation of the input signal. This independent time-domain representation is thus similar to the frequency-domain representation. However, unlike the conventional frequency-domain circuit parameters, which relate voltage and current amplitudes, the time-domain circuit representation is based on incident and reflected wave-type constituents. In addition, the use of appropriate norms facilitates the transformation of our operators to stand-alone figures of merits. The general concepts developed are demonstrated for a short dipole antenna View full abstract»

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  • Analysis and measurements for improved crank-line antennas

    Publication Year: 1997 , Page(s): 1166 - 1172
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    This paper describes the radiation characteristics of crank-line antennas radiating a circularly polarized wave. First, the radiation efficiency versus substrate permittivity is evaluated. Second, a 12-cell crank-line antenna of substrate permittivity εr=1 and antenna height B=λ11.85 is investigated as a reference antenna, where λ11.85 is the wavelength at a frequency of 11.85 GHz. It is found that the main beam direction of the reference antenna varies 7° over a frequency range of approximately 6%, with an axial ratio of less than 3 dB and a gain of approximately 21 dB. Third, attention is paid to the gain behavior versus the antenna height. A way to increase the gain by modifying the antenna height is proposed. An increase of 1.5 dB from the gain of the reference antenna is demonstrated. Finally, the axial ratio, gain, and decoupling factor for crank-line antenna arrays are presented and discussed View full abstract»

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  • Path diversity for LEO satellite-PCS in the urban environment

    Publication Year: 1997 , Page(s): 1107 - 1116
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    A new method for analyzing the propagation aspects of mobile satellite systems is introduced. It consists of: (1) taking fisheye lens images at potential user locations; (2) extracting path state information (clear, shadowed, or blocked) as a function of look angles from the images; and (3) combining each path state for single or multiple satellites in a specific constellation with frequency-appropriate statistical fade models to predict overall performance measures such as fade dependence with elevation angle or path-diversity gain. The advantage of the method is that it minimizes the need for expensive propagation campaigns. The importance of including specular reflections and diffraction under urban blockage conditions is established. From images obtained in urban Japan, a fade-lapse rate with elevation of 0.2 dB/degree is deduced for fades exceeded about 10% of the time. Path-diversity gain for combining and hand-off diversity is found for up to four-fold diversity at a high-, mid-, and low-latitude location for the Globalstar constellation. With two-fold diversity and neglecting implementation losses, the fade margin required for 80% and 95% coverage at mid-latitude urban locations is reduced from 16 to 6 dB and from 25 to 16 dB, respectively View full abstract»

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  • Experimental investigations into a linearly polarized radial slot antenna for DBS TV in Australia

    Publication Year: 1997 , Page(s): 1123 - 1129
    Cited by:  Papers (45)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    A hybrid theoretical/experimental approach to the design of radial line slot array (RLSA) antennas for receiving direct broadcast satellite (DBS) TV programs in Australia is presented. Using this approach, 0.4-m and 0.6-m diameter linearly polarized Ku-band prototype antennas were constructed and experimentally investigated. The 0.6-m prototype incorporates reflection cancelling slots, which allow it to overcome the inherent poor return loss performance in linearly polarized RLSA antennas. Measurements show high-radiation efficiency for this form of radial slot antenna and its suitability for the DBS TV application View full abstract»

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  • Scattering from a cylindrically conformal slotted waveguide array antenna

    Publication Year: 1997 , Page(s): 1150 - 1159
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (876 KB)  

    A numerical method is developed to investigate electromagnetic scattering by a cylindrically conformal waveguide-fed slot array. The problem is first formulated in terms of integral equations using the equivalence principle. The integral equations are then solved using the method of moments (MoM) in conjunction with global sinusoidal basis functions and Galerkin's testing procedure. The MoM solution requires the evaluation of the generalized admittance matrices involving various dyadic Green's functions. The slow convergence of the series associated with the summation of waveguide modes is accelerated using the Kummer transformation and the slow convergence of the series associated with the summation of the exterior modes is avoided by using the asymptotic solutions with proper treatment for singular integrals. The evaluation of the excitation vector and scattered field is also accelerated using Watson's transformation and asymptotic solutions. Numerical results are presented to illustrate the scattering characteristics of the cylindrically conformal waveguide-fed slot arrays, such as the effects of curvature, slot thickness, and waveguide termination on the radar cross section (RCS) of the arrays View full abstract»

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  • The hexagonal horn as an efficient Gaussian beam launcher

    Publication Year: 1997 , Page(s): 1173 - 1178
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    A new type of feed horn-the hexagonal horn-is proposed and investigated by means of Gaussian-Hermite beam-mode analysis. The electric-field distribution at the horn aperture plane is approximated. The polarization efficiency is 88.66%. The fractional power in the fundamental beam mode is about 85%. The near- and far-field radiation patterns are calculated. The high fractional power in the fundamental beam mode of the horn indicates that it can be used as an efficient Gaussian beam launcher in quasi-optical systems View full abstract»

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  • Measurements and predictions of the RCS of Bruderhedrals at millimeter wavelengths

    Publication Year: 1997 , Page(s): 1071 - 1079
    Cited by:  Papers (4)
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    Polarimetric radar cross sections (RCSs) were measured for two large Bruderhedrals at 35 and 93 GHz. The overall spread in the measured RCS was 2 dB. It was found that the absolute RCS as well as the dependence of the RCS on elevation angle could be significantly altered by a slight misalignment of the Bruderhedral. The calculations of these RCSs by theories for a top hat and RCS simulation codes based on geometric and physical optics (PO) generally agreed with the measurements to within 3 db. Radar calibrations using these Bruderhedrals that are based on the predictions are not reliable, however, if accuracies better than 3 dB are required, The measured values of the cross-polarization RCS were very small compared to the copolarization ones, consistent with the codes and theoretical considerations View full abstract»

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  • Iterative least-squares synthesis methods for conformal array antennas with optimized polarization and frequency properties

    Publication Year: 1997 , Page(s): 1179 - 1185
    Cited by:  Papers (44)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    An iterative least-squares synthesis technique is presented for the optimization of the element excitation in conformal array antennas. This method allows the designer to have predefined goals for the shaped radiation pattern over a selected frequency band and for the polarization properties of the array. Linear or circular polarization can be used in the synthesis. Different kinds of synthesis goals can be set, whereby the copolarization or cross-polarization properties of the array are weighted or a narrowband or wideband design is sought. The amplitudes of the element excitations can be fixed. Several synthesis examples are presented for an array on a sphere with circular polarized elements. Broad-band and low cross-polarization designs are included View full abstract»

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  • Stripline-fed arbitrarily shaped printed-aperture antennas

    Publication Year: 1997 , Page(s): 1186 - 1198
    Cited by:  Papers (27)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    A full-wave analysis method is presented for modeling the radiation properties of a stripline-fed planar printed-aperture antenna element. In this formulation, both the finite length of stripline and the finite aperture may be of any arbitrary shape since their equivalent electric and magnetic currents are modeled with triangular patch basis functions. Galerkin's method is applied to numerically solve the coupled mixed-potential integral equation (MPIE). Exact spatial-domain Green's functions are used to account for all radiation, surface-wave, and mutual-coupling effects. Interactions between the stripline feed and the radiating aperture are rigorously included. Numerical analysis is presented for the following nonrectangular shapes: an exponentially tapered slot, an annular slot, an annular slot with opposing stubs, and a monofilar Archimedean spiral slot element. Results are shown for input return loss, radiation patterns, and axial ratio for the circularly polarized elements View full abstract»

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  • G/T maximization of a paraboloidal reflector fed by a dipole-disk antenna with ring by using the multiple-reflection approach and the moment method

    Publication Year: 1997 , Page(s): 1130 - 1139
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    A 1.8-m paraboloidal reflector fed by a dipole-disk antenna with a beamforming ring is optimized for high G/T at L-band by using the moment method (MM) and the multiple reflection (MR) approach. The MR approach is based on using MM to calculate the radiation and scattering patterns of the feed, using physical optics plus uniform geometrical theory of diffraction (UTD) to include the reflector, and in addition to include the mutual interaction (multiple reflections) between the reflector and the feed by using the expression for the sum of an infinite geometric series. The MR approach is shown to be equally accurate as a MM solution of the complete antenna with reflector, provided the reflector is in the far field of the feed, and the MR approach is much faster. As a result of the calculations using the MR approach, design curves are presented showing how the G/T varies as a function of antenna geometry, size, and elevation angle, all for a given noise profile of the surrounding sky and ground. The computed radiation patterns and G/Ts are compared with measurements for several elevation angles and surrounding terrain View full abstract»

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  • Reflection and transmission characteristics of single-layer periodic composite structures for TE case

    Publication Year: 1997 , Page(s): 1065 - 1070
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    A periodic surface-integral formulation is proposed to analyze the reflection and transmission characteristics of a single-layer lossy periodic composite structure for the TE case. Theoretically, the equivalence principle, involving unknown electric and magnetic currents over material discontinuity interfaces, the structure periodicity, and the Poisson summation formula are used to reduce the problem to a periodic cell. These surface-integral equations are solved numerically by the method of moments with pulse bases and point matching. In this study, the numerical results such as reflected, transmitted, and dissipated powers for a single-layer graphite/epoxy composite structure with both circular and square fibers are presented for the TE case. The effects of frequency, incident angle, fiber area, fiber conductivity, and embedding dielectric etc. are examined in detail. Convergence study and comparison with the previous published results are also included to confirm the accuracy of the new formulation 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