By Topic

Antennas and Propagation, IEEE Transactions on

Issue 4 • Date April 2003

Filter Results

Displaying Results 1 - 25 of 36
  • Comments on "Resonant frequencies of rectangular microstrip antennas with flush and spaced dielectric superstrates"

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (150 KB)  

    The author comments that the work of Bernhard and Tousignant (see IEEE Trans. Antennas Propagat., vol.47, p.302-308, Feb. 1999) is important for implementations in computer-aided design (CAD). The authors have successfully tied up many loose ends in the previously reported work in this area. However, it appears they have not been attentive to include the effect of the dielectric thickness for the substrate with relative permittivity /spl epsi//sub 3/. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • List of reviewers for 2001 and 2002

    Page(s): 919 - 922
    Save to Project icon | Request Permissions | PDF file iconPDF (150 KB)  
    Freely Available from IEEE
  • A cross-polarized bistatic calibration device for RCS measurements

    Page(s): 833 - 839
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (510 KB) |  | HTML iconHTML  

    A little known unidirectionally conducting canonical object is introduced, which satisfies the requirements for use as a cross-polarized bistatic calibration device, including a signature with the desirable property of being able to be characterized analytically. Bistatic measurements are essential to understanding the stealth characteristics of military targets, and since no similar cross-polarization calibration target is available, the proposed device shows potential for becoming a new radar cross section (RCS) measurement standard. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An on-site dosimetry system for safety assessment of wireless base stations using spatial harmonic components

    Page(s): 840 - 847
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (497 KB) |  | HTML iconHTML  

    Most of the recently revised safety limits worldwide are set in terms of the limits of rates of internal energy deposition [specific absorption rates (SARs)] for radio/microwave frequencies. Since procedures to ascertain compliance with the SAR limits are cumbersome, requiring complex computer modeling or bulky, mostly homogenous experimental phantoms, they are ignored in favor of easy-to-measure incident fields. Radio-frequency (RF)/microwave installations are thus erroneously declared safety compliant or not based solely on the measured incident fields. A rapid "real-time" SAR determination system is also needed to define the safety zone for RF/microwave installations such as wireless base stations. We describe an approach where the measured incident electric (E) fields (both vertical and horizontal components) for an imaginary vertical plane of dimension 0.96×2.28 m in the immediate vicinity of the intended location of the human may be used to obtain whole-body-average and peak 1- or 10-g SARs using a portable PC in less than one minute of compute time. The method relies on describing the measured E fields in terms of space harmonic components and using the prestored solutions for the internal E-fields (Ex,Ey,Ez) for the various voxels of the human body model for six to ten strongest harmonic components. This approach has been validated using examples of commercial base-station antennas both at 835 and 1900 MHz, elevated or not, for varying distances (1-10 m) of the human model from such antennas. The whole-body-average and peak 1-g SARs are less than 5-10% different than those obtained using the computationally intensive full finite-difference time-domain (FDTD) simulations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Author's reply [to comments on "Resonant frequencies of rectangular microstrip antennas with flush and spaced dielectric superstrates"]

    Page(s): 917 - 918
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    Bernhard and Tousignant (see IEEE Trans. Antennas Propagat., vol.47, p.302-308, Feb. 1999) replies that Mishra's (see IEEE Trans. Antennas and Propagat., vol.51, no.4, p.917, 2003) makes the point that we do not consider the thickness of the spaced superstrate in the theoretical formulation. We already note this detail. The goal of the paper is to provide a closed-form model to predict the resonant frequency of a microstrip antenna with a spaced superstrate as accurately as possible given the tolerance ranges of the structure's electrical and physical parameters. For materials with relative permittivities less than 3, the data suggest that the thickness of the superstrate can be neglected without loss of accuracy in light of these tolerances. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A reciprocity approach for calculating radiation patterns of arbitrarily shaped microstrip antennas mounted on circularly cylindrical platforms

    Page(s): 730 - 738
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (787 KB) |  | HTML iconHTML  

    The paper presents a convenient and efficient approach, based on the reciprocity theorem, for calculating the radiation patterns of arbitrarily shaped microstrip antennas with dielectric substrate and superstrate layers mounted on circularly cylindrical platforms. A detailed theoretical development followed by examples with numerical and graphical results illustrate the versatility of the technique. The reciprocity approach presented is very flexible and may be used in conjunction with any of the commonly employed computational electromagnetics modeling approaches such as the method of moments, finite-element methods, and finite-difference time-domain techniques. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Neurofuzzy classification and rule generation of modes of radiowave propagation

    Page(s): 862 - 871
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (772 KB) |  | HTML iconHTML  

    This paper describes, in a neurofuzzy framework, a method for the classification of different modes of radiowave propagation, followed by generation of linguistic rules justifying a decision. Weight decay during neural learning helps in imposing a structure on the network, resulting in the extraction of logical rules. Use of linguistic terms at the input enables better human interpretation of the inferred rules. The effectiveness of the system is demonstrated on radiosonde data of four different seasons in India. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Maximum electromagnetic coupling to a nearby conducting strip through narrow and wide slits in a parallel-plate waveguide

    Page(s): 693 - 699
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB) |  | HTML iconHTML  

    The problems involved in electromagnetic coupling to a nearby conducting strip through narrow and wide slits in a parallel-plate waveguide (PPW) are discussed as simplified models of the two-dimensional (2-D) problems of aperture-coupled and proximity-coupled microstrip structures while focusing on radiative coupling mechanisms and perfect matching methods. These matching mechanisms exemplify general matching methods for use in small flush antenna structures. Finally, the similarity between the role of the nearby strip and the phasing unit of the recently reported crossed-field antenna structure is also discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Efficient analysis of input impedance and mutual coupling of microstrip antennas mounted on large coated cylinders

    Page(s): 739 - 749
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (817 KB)  

    An efficient and accurate hybrid method, based on the combination of the method of moments (MoM) with a special Green's function in the space domain is presented to analyze antennas and array elements conformal to electrically large material coated circular cylinders. The efficiency and accuracy of the method depend strongly on the computation of the Green's function, which is the kernel of the integral equation that is solved via MoM for the unknown equivalent currents representing only the antenna elements. Three types of space-domain Green's function representations are used, each accurate and computationally efficient in a given region of space. Consequently, a computationally optimized analysis tool for conformal microstrip antennas is obtained. Input impedance of various microstrip antennas and mutual coupling between two identical antennas are calculated and compared with published results to assess the accuracy of this hybrid method. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of asymptotic theory of differential phase millimeter-wave scintillations in the oxygen absorption region

    Page(s): 872 - 879
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    This paper presents a model for dual frequency differential phase scintillations for a plane wave propagating through a turbulent medium characterized by a complex refractive index. In contrast to the predicted enhancement of the low-frequency portion of the amplitude spectrum by absorption fluctuations, our theoretical model predicts that the absorption mechanism has virtually no significant effect on the absolute phase spectrum, but can enhance the differential phase spectrum at intermediate frequencies when the propagation frequencies are very close. The effect of turbulence scale size is also analyzed. Experimental differential phase spectra agree well with the theoretical models presented here. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Tunnel diode-loaded rectangular microstrip antenna for millimeter range

    Page(s): 750 - 755
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (519 KB) |  | HTML iconHTML  

    Theoretical investigations conducted for Ge tunnel diode-integrated rectangular patch antenna reveals that such an antenna exhibits frequency tunability with the bias voltage. The Ge tunnel diode-loaded patch can be operated in the millimeter range (51.042-54.013 GHz). The range of frequency obtainable for operation is 2971 MHz. The radiation pattern shows variation with the bias voltage and the radiated power, the beamwidth and the directivity vary inversely with the bias voltage. Thus, the Ge tunnel diode-loaded patch can be used to achieve electronic tuning (BW=5.66%) with the bias voltage. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A broad-band CPW-fed strip-loaded square slot antenna

    Page(s): 719 - 721
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (453 KB) |  | HTML iconHTML  

    A novel broadband design of a coplanar waveguide fed square slot antenna loaded with conducting strips is proposed and experimentally studied. The obtained results show that the impedance bandwidth, determined by 10-dB return loss, of the proposed slot antenna can be greater than 60%. The design considerations for achieving broad-band operation of the proposed slot antenna are described, and experimental results are presented. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cloud-induced effects on monthly averaged scintillation amplitude along millimeter-wave slant paths

    Page(s): 880 - 887
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (471 KB) |  | HTML iconHTML  

    A physical-statistical analysis of cloud-induced effects on millimeter-wave amplitude scintillation along Earth-satellite slant paths is presented. Using numerical simulations derived from a cloud radiative model, a dual-channel nonlinear retrieval algorithm is set up to estimate simultaneously cloud columnar water vapor and liquid water contents from measured ground-based brightness temperatures. The latter are related in cloudy conditions to surface meteorological variables and columnar water vapor and liquid water contents. ITALSAT ground-station data consisting of time series of beacon scintillation at 18.7, 39.6, and 49.5 GHz, surface meteorological data and radiometric observations at 13.0, 23.8, and 31.6 GHz, are used for an experimental analysis of cloud-induced scintillation by selecting a period of six years from 1994 to 1999. The results show a significant correlation between amplitude scintillation variances and cloud columnar contents on a monthly basis (i.e., averaged on-time intervals of one month). Considerations about possible impact of this analysis on the development of scintillation prediction models are finally illustrated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Thinned coincident arrays for the direct measurement of the principal solution in radio astronomy

    Page(s): 788 - 793
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (455 KB) |  | HTML iconHTML  

    A new technique is described for the design of a thinned, linear, multiplicative array which directly measures the principal solution of a radio source distribution. The original filled multiplicative array with uniform element spacing ℓ is first generalized to an array of N1+1 subarrays each with M1+1 elements. A thinning factor of 1/2 is shown to be possible if M1=N1. Finally, if each subarray is further divided into smaller subarrays until the smallest are simply two element interferometers, then the principal solution can be directly measured but with far fewer elements. Significant thinning factors are achieved when the array is very large. The method can also be used to measure the principal solution with planar arrays, with very strong thinning occurring for large arrays. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Comparison of random phasing methods for reducing beam pointing errors in phased array

    Page(s): 782 - 787
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB) |  | HTML iconHTML  

    Beamsteering for phased arrays normally causes a pointing deviation of the main beam due to the periodic phase quantization error across the array. This deviation occurs due to the use of digital phase shifters. We modify the random phasing methods into appropriate random phasing methods, in which the accuracy of the pointing direction in phased arrays is improved. The word "appropriate" means that, for the phase quantization error, the rounding to the nearest bit method is not always to be applied, nor is the random phasing method. An appropriate mean phase error equal-to-zero method (AMPEEZ), an appropriate two probable value method (A2PV) and an appropriate phase-added method (APAM) are proposed. These methods are simulated and compared with the nonappropriate ones. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Scattering from multiple objects buried beneath two-dimensional random rough surface using the steepest descent fast multipole method

    Page(s): 802 - 809
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2097 KB)  

    Generalized formulations are presented to analyze the electric field scattered from multiple penetrable shallow objects buried beneath two-dimensional random rough surfaces. These objects could have different materials, shapes, or orientations. In addition, their separation distance may range from a fraction of a wavelength to several wavelengths. The fast algorithm, steepest descent fast multipole method (SDFMM), is used to compute the unknown electric and magnetic surface currents on the rough ground surface and on the buried objects. Parametric investigations are presented to study the effect of the objects proximity, orientations, materials, shapes, the incident waves polarization, and the ground roughness on the scattered fields. A significant interference is observed between the objects when they are separated by less than one free space wavelength. Even when the clutter due to the rough ground is removed, the return from the second object, can be dominating causing a possible false alarm in detecting the target. The results show that the distortion in target signature significantly increases with the increase of both the proximity to a clutter item and the ground roughness. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Pattern characteristics of linear arrays using the constrained least squares distribution

    Page(s): 772 - 775
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (285 KB)  

    The constrained least squares (CLS) distribution is a method for obtaining distribution functions that yield low sidelobe patterns with specified constraints on the aperture efficiency, and are especially useful for the transmit patterns of active array antennas. The widely used Taylor distribution optimizes only pattern performance while the CLS distribution optimizes pattern performance while taking into account the constraints on both the peak element amplitude and the total effective radiated voltage (ERV) of the aperture distribution. The paper compares the pattern characteristics of linear arrays with CLS and Taylor distributions. The results help to establish guidelines on when a CLS distribution would be preferable over a Taylor distribution when a specified aperture efficiency is important. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effect of AR model-based data extrapolation on target recognition performance

    Page(s): 912 - 914
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (230 KB) |  | HTML iconHTML  

    A data extrapolation method is applied to improve the performance of a target recognition scheme based on the central moments of one-dimensional range profiles. We adopt the autoregressive (AR) model to extrapolate the radar cross section data of a target in order to expand the measured data window. It is shown that the resulting high resolution range profiles can enhance target recognition capability, providing a more accurate recognition performance than the multiple signal classification range profile for moderate signal-to-noise ratio SNR ranges. Furthermore, the effects of the AR model-based data extrapolation on target recognition accuracy are carefully analyzed and investigated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Temporal Mueller matrix solution for polarimetric scattering from inhomogeneous random media of nonspherical scatterers

    Page(s): 820 - 832
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1110 KB) |  | HTML iconHTML  

    Polarimetric scattering from inhomogeneous random media of nonspherical scatterers under a pulse incidence is studied. The time-dependent Mueller matrix solution of vector radiative transfer for layering random media is derived. Copolarized and cross-polarized bistatic and back- scattering are numerically calculated. The shape and intensity of polarized echoes well depict the inhomogeneous fraction profile of random scatterers. Its functional dependence upon the fraction profile, layering thickness, and other parameters are discussed. This technique is applicable to reconstruction of inhomogeneous fraction profile and inversion of the media thickness. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An efficient computation scheme for the free space Green's function of a two-dimensional semiinfinite phased array

    Page(s): 766 - 771
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB) |  | HTML iconHTML  

    A simple scheme is developed to compute the Green's function of a periodic semiinfinite array in free space. It is based on the spectral representation of the fields radiated by an infinite linear array of dipoles. Results related to successive linear arrays are added in the space domain. This summation can be accelerated tremendously by using an elementary extrapolation technique. The resulting formulation converges everywhere in the plane containing the array, and the number of terms required to achieve a given precision increases slowly away from this plane. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiband multiple ring monopole antennas

    Page(s): 722 - 729
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    This paper proposes two novel designs of a multiband antenna using multiple rings. The first design consists of a set of self-similar circular rings. This is an alternative to the recently reported triangular fractal Sierpinski gasket monopole antenna, and comparison is made to this and the circular disk monopole antenna. The second design is realized by varying the shape of the circular structure to an elliptical one. Larger bandwidth and improved patterns are achieved. In comparison to the circular disk, improved radiation pattern control at higher operating bands, due to the discrete structure of the multiple rings, is shown by numerical and experimental results. The bandwidth is significantly larger than the Fractal Sierpinski gasket and Parany monopole. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two-dimensional scattering center extraction based on multiple elastic modules network

    Page(s): 848 - 861
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (866 KB) |  | HTML iconHTML  

    The concept of scattering centers on a target is commonly used for radar signature modeling and data compression, as well as target recognition. In particular, two-dimensional (2-D) scattering centers are useful features in automatic target recognition, which uses a synthetic aperture radar system, because they are directly related to physical scattering mechanisms and also have small dimensionality. We propose a new technique for estimating 2-D scattering centers using radar data in the frequency-aspect domain. The technique first estimates one-dimensional scattering centers at several aspects, and the multiple elastic modules network optimization is exploited to find 2-D locations and amplitudes of the target's scattering centers. Experimental results illustrate that the proposed method is efficient not only for estimating 2-D scattering centers on the target but also in computation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fundamental modal phenomena on isotropic and anisotropic planar slab dielectric waveguides

    Page(s): 888 - 897
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (654 KB) |  | HTML iconHTML  

    The characteristic interactions of discrete modes supported by planar isotropic and anisotropic dielectric slab waveguides are analyzed using singularity and critical point theory, leading to a rigorous and complete explanation of all modal interactions. Complex frequency-plane singularities associated with modes on isotropic waveguides are identified and discussed, and the absence of mode coupling is proven. For an anisotropic planar waveguide having an arbitrarily oriented optical axis, it is shown that mode coupling is controlled by the presence of an isolated Morse critical point (MCP) accompanied by a pair of complex-conjugate frequency-plane branch points. The interaction of space-wave leaky modes on a grounded anisotropic slab is studied by investigating the evolution of complex frequency-plane branch point singularities as the orientation of the optical axis varies. The general theory is presented, and numerical results are provided for some specific waveguides. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Investigation of the mutual coupling between apertures on doubly curved convex surfaces: theory and measurements

    Page(s): 682 - 692
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1198 KB) |  | HTML iconHTML  

    A hybrid method of high-frequency approximation (UTD) and method of moments is used to calculate the mutual coupling between circular apertures on a doubly curved surface. This requires that the geodesics on doubly curved surfaces be found. To represent the aperture fields, a single waveguide mode approximation is used. In order to verify the theoretical results, a general paraboloid of revolution with circular waveguide-fed apertures was built at Ericsson Microwave Systems AB, Molndal, Sweden. This has given a possibility to verify the theoretical model for a general doubly curved surface against measurements. To the authors' knowledge, no such verification is available in the literature. It was found that measured and theoretical results in terms of mutual coupling agree very well for copolar coupling. As expected, the mutual coupling results are very dependent on the polarization. In fact, the definition of polarization directions and the need for polarization control are important issues for doubly curved conformal array antennas. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A cavity-backed rectangular aperture antenna with application to a tilted fan beam array antenna

    Page(s): 712 - 718
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1141 KB) |  | HTML iconHTML  

    A rectangular aperture of Ax×Ay, cut in the top conducting plate of a triplate transmission line and backed by a cavity, radiates a tilted beam off the direction normal to the aperture. The mechanism of the radiation is explained using the Poynting vector distribution above the aperture and the phase distribution of the electric field over the aperture. The tilt angle is calculated as a function of side length Ax for a representative value of Ay=18 mm=0.747λ12.45, where λ12.45 is the wavelength at a test frequency of 12.45 GHz. A tilted beam of approximately 27° is realized at Ax/Ay=8/9 with a gain of approximately 8 dB. Using this value of Ax/Ay, an array antenna composed of rectangular cavity-backed aperture elements is investigated. The array forms a tilted fan beam without phase shifters. The frequency responses of the gain and input impedance are discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief                                                 Kwok W. Leung