By Topic

Antennas and Propagation, IEEE Transactions on

Issue 7 • Date Jul 1995

Filter Results

Displaying Results 1 - 19 of 19
  • Simultaneous measurements of L- and S-band tree shadowing for space-Earth communications

    Page(s): 713 - 719
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    This paper presents results from simultaneous L- and S-band slant-path fade measurements through a pecan, a cottonwood, and a pine tree employing a tower-mounted transmitter and dual-frequency receiver. A single circularly polarized antenna was used at each end of the link. The objective was to provide information for personal communications satellite uplink power control design on the correlation of tree shadowing between frequencies near 1620 and 2500 MHz. Fade time series obtained simultaneously did not exhibit any significant correlation, but their means were weakly correlated (r2 from 0.31 to 0.58). Fades were measured along a 10-m lateral distance with 5-cm spacing. Instantaneous fade differences between L- and S-band exhibited a normal distribution with means usually near 0 dB and standard deviations from 5.2 to 7.5 dB. The cottonwood tree was an exception with 5.4 dB higher average fading at S- than at L-band. More than 90% of the spatial variations occurred with periods larger than 1~2 wavelengths. Simultaneous swept measurements over 160-MHz spans showed that the standard deviation of the power levels as function of frequency increased from about 1 dB at locations with mean fades less than 4 dB to near 6 dB at locations with mean fades of 20 dB. For a 5-dB fade, the central 90% of fade slopes were within a band of 0.7 dB/MHz at L- and 1.9 dB/MHz at S-band View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Integral equation analysis of dielectric and conducting bodies of revolution in the presence of arbitrary surfaces

    Page(s): 674 - 680
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    A formulation is developed to treat radiation from structures consisting of conducting and/or dielectric bodies of revolution (BOR) in the presence of multiple arbitrary shaped three-dimensional objects. A set of integral equations is developed on the surfaces of the combined structure and the resulting integro-differential equations are solved using the method of moments. On the BOR, harmonic entire domain expansion functions are used for the circumferential dependence, while overlapping sub-domain functions are used to model axial curvature. The arbitrary shaped portions of the structure are modeled using triangular surface patch basis functions. The resulting matrix has a partial block diagonal nature which provides a more economical solution for structures which have some rotational symmetry. The accuracy of the BOR and arbitrary surface formulation is verified using the self-consistency method and measured data View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Complex source representation of time harmonic radiation from a plane aperture

    Page(s): 720 - 723
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Developed here is a new complex source representation for time harmonic radiation from a plane aperture which is the Kirchhoff's spatial convolution formula of a complex plane aperture with the complex aperture field being the analytic extension of the original aperture field. A systematic study for a one-dimensional linearly phased cosine aperture distribution confirms the effectiveness of the new method in the simulation of the time harmonic radiation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improvement of the Rayleigh approximation for scattering from a small scatterer

    Page(s): 681 - 688
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    An improvement of the Rayleigh approximation for electromagnetic scattering from an arbitrary small scatterer is developed through solving the conventional integro-differential equation governing the electric field inside the scatterer. The improvement is represented by an equivalent polarizability tensor differing from that used in the Rayleigh approximation in two aspects: (i) it is frequency dependent, and (ii) it gives a scattering amplitude tensor satisfying energy conservation. The energy conservation is investigated through formulating the extinction, scattering, and absorption losses according to the equivalent polarizability tensor. Numerical calculations on spheres and spheroids indicate that the present extinction loss formulation has a wider validity range than the extinction loss formulation according to the Rayleigh approximation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An exact line integral representation of the physical optics scattered field: the case of a perfectly conducting polyhedral structure illuminated by electric Hertzian dipoles

    Page(s): 689 - 696
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    An exact line integral representation of the electric physical optics scattered field is presented. This representation applies to scattering configurations with perfectly electrically conducting polyhedral structures illuminated by a finite number of electric Hertzian dipoles. The positions of the source and observation points can be almost arbitrary. The line integral representation yields the exact same result as the conventional surface radiation integral; however, it is potentially less time consuming and particularly useful when the physical optics field can be augmented by a fringe wave contribution as calculated from physical theory of diffraction equivalent edge currents. The final expression for the line integral representation is lengthy but involves only simple functions and is thus suited for numerical calculation. To illustrate the exactness of the line integral representation, comparisons of numerical results obtained from the surface and the line integral representations are performed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Improving the scan performance of probe-fed microstrip patch arrays on high dielectric constant substrates

    Page(s): 705 - 712
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    This paper presents a thorough investigation into the use of E-plane parasitic elements to remove scan blindness in probe-fed microstrip patch phased arrays using a rigorous full-wave analysis. It is shown that the addition of an E-plane parasitic element in the unit cell of the array can enhance the impedance scanning range; however, the parasitic element must be resonating. As a consequence of this, the method of scan blindness removal is only suited to microstrip patch arrays mounted on high dielectric constant material. A novel configuration incorporating a varactor diode to reduce the significant reactive nature of the input impedance at large scan angles is introduced which further improves the scanning potential of the parasitic element array. A further modification to the unit cell is proposed which allows the array to operate over a broad frequency range. For all the configurations considered, comparisons of active reflection coefficient, scan impedance behavior, efficiency, and cross-polarization levels are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A procedure for synthesizing a specified sidelobe topography using an arbitrary array

    Page(s): 742 - 745
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    A simple method to arrive at an optimum set of array excitations to achieve a specified radiation pattern is presented. An auxiliary function is formulated, based on the envelope of the required sidelobe structure and the array factor, in the sidelobe region. This function is minimized, subject to the main lobe constraints and the null steering constraints, to determine the excitations. An iterative procedure is used to generate the desired pattern, with the additional constraints like sidelobe level, symmetric excitation, and so on. The method has been successfully applied to synthesize linear arrays and circular arc arrays and to generate symmetric as well as asymmetric patterns View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Complementary operators: a method to annihilate artificial reflections arising from the truncation of the computational domain in the solution of partial differential equations

    Page(s): 697 - 704
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    The ease and simplicity with which the finite difference time domain (FDTD) or the finite elements (FE) techniques can handle complex radiation or scattering problems have lead to a remarkable surge in the use of these methods. While execution time is becoming less of an impediment when solving large problems, the biggest constraint remains the memory needed to run the FDTD or the FE methods. It is precisely this limitation that the article addresses. A boundary operation is developed to minimize the artificial reflections that arise when truncating the computational domain of an open region scattering or radiation problem. The method is based on the use of two boundary operators that are complementary in their action. By solving the problem with each of the two operators and then averaging the two solutions, the first-order reflections that arise from the artificial boundary can be completely eliminated. Numerical results are presented to show that this new technique gives significant reduction in the error when compared to other widely used boundary conditions View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A fast algorithm for signature prediction and image formation using the shooting and bouncing ray technique

    Page(s): 727 - 731
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    We present a fast simulation algorithm for generating the range profiles and inverse synthetic aperture radar (ISAR) images of complex targets using the shooting and bouncing ray (SBR) technique. Starting with the time-domain and image-domain ray-tube integration formulas we derived previously, we cast these formulas into a convolution form. The convolution consists of a nonuniformly sampled signal and a closed-form time-domain or image-domain ray spread function. Using a fast scheme proposed by Sullivan (1990), the nonuniformly sampled function is first interpolated onto a uniform grid before the convolution is performed by the fast Fourier transform (FFT) algorithm. Results for several complex targets are presented to demonstrate the tremendous computation time savings and excellent fidelity of the scheme. Using the fast scheme, a speed gain of a factor of 30 is achieved in performing the ray summation as compared to the direct convolution in range profile computation and a factor of 180 in ISAR image formation for a typical aircraft at S-band View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • FDTD analysis of nonlinear magnetic diffusion by reduced c

    Page(s): 653 - 659
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    The finite-difference time-domain (FDTD) approach is a particularly useful method for investigating nonlinear electromagnetics because the nonlinear relationships may be directly incorporated into the equation for advancing the electromagnetic fields. This approach is applicable to nonlinear magnetic materials with or without hysteresis (i.e. time dependence). Problems with geometric details that are very small compared to signal wavelengths, however, stress FDTD techniques. This occurs because the Courant-limited Δt can become small enough to require the use of >1011 time steps unless one is tricky. Tricky means observing that this sort of problem has a solution which seldom depends on the speed of light c. Here, we demonstrate a procedure to elude the Courant stability condition by defining c to be 100 m/s. The present problem arose out of a magnetic diffusion FDTD application. The “reduced-c” technique should work, however, for any problem where Δt is limited by Δx/c which, in turn, is limited by the smallness of the problem geometry, not by a need for extremely fine temporal electromagnetic resolution View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Single and stacked circular microstrip patch antennas backed by a circular cavity

    Page(s): 746 - 750
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    In this communication, a full wave moment method solution for a probe-fed circular microstrip patch antenna, backed by a circular cavity both in single and in stacked configurations, is used to analyze the effect of a parasitic patch on antenna bandwidth. In addition, the effect of recessing a single patch into the antenna cavity is studied. In both cases, theoretical results for the scattering and radiation characteristics of the antenna are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An efficient implementation of surface impedance boundary conditions for the finite-difference time-domain method

    Page(s): 660 - 666
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    An efficient way to implement the surface impedance boundary conditions (SIBC) for the finite-difference time-domain (FDTD) method is presented in this paper. Surface impedance boundary conditions are first formulated for a lossy dielectric half-space in the frequency domain. The impedance function of a lossy medium is approximated with a series of first-order rational functions. Then, the resulting time-domain convolution integrals are computed using recursive formulas which are obtained by assuming that the fields are piecewise linear in time. Thus, the recursive formulas derived here are second-order accurate. Unlike a previously published method [7] which requires preprocessing to compute the exponential approximation prior to the FDTD simulation, the preprocessing time is eliminated by performing a rational approximation on the normalized frequency-domain impedance. This approximation is independent of material properties, and the results are tabulated for reference. The implementation of the SIBC for a PEC-backed lossy dielectric shell is also introduced View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dual-polarization slot-coupled printed antennas fed by stripline

    Page(s): 738 - 742
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    This article presents recent techniques in the field of dual-polarization printed antennas for designing shielded radiating structures with high-quality performances in terms of cross-polarization level and input-port isolation. The use of gridded patches provides a natural solution to filtering surface currents and is of key importance in limiting inter-element coupling in arrays. Experimental results obtained on various designs are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Surface reflection at low-angle propagation

    Page(s): 639 - 652
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1228 KB)  

    A new derivation of the ground-reflection coefficient based on rough-surface scattering theory is proposed to predict surface mechanism effects on both overwater and overland microwave line-of-sight links. A detailed model of diffused scattering is constructed which agrees in part with available experimental data and monostatic radar measurements. The model allows one to take into account the effects of antenna directivity, refraction by superrefractive layers, and various types of vegetation cover. Using this model, it is shown that atmospheric and surface mechanisms cannot be dissociated in estimating the ground reflection coefficient and that, on terrestrial links, it is necessary to introduce any forests as part of the terrain profile to estimate as accurately as possible the specular and the scattering reflection coefficients View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Lateral wave contribution to the radiation from a dielectric half medium

    Page(s): 751 - 755
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Two methods are presented for the computation of the radiation at microwave frequencies in a thin dielectric medium from a source located in a dense dielectric medium. One is based on geometrical optics and the other on physical optics. The geometrical optics approach encounters some difficulties in the evaluation of the radiation in the thin dielectric medium near grazing-incidence condition, due to excitation of a lateral wave, which is not taken in consideration by this approach. The physical optics method, which considers the lateral wave contribution, approaches this problem successfully and gives a better approximation of the radiated field near grazing. Numerical results, which compare the two methods, and experimental data are offered to validate the theoretical approach View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Admittance of a longitudinal waveguide slot radiating into an arbitrary cylindrical structure

    Page(s): 667 - 673
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    In this paper we use a hybrid method to calculate the admittance of a longitudinal slot (of finite length) in a rectangular waveguide, when the slot radiates into a cylindrical outer structure of arbitrary finite cross section. The analysis takes advantage of a Fourier transformation along the cylinder axis, by which the computational effort is drastically reduced. The harmonic spectral currents on the structure are expanded in subsectional triangular basis functions and determined using an electric field integral equation (EFIE) and the moment method. These currents and the corresponding fields are inverse Fourier transformed and matched over the slot to the fields inside the waveguide by an additional moment method approach using entire domain basis functions for the slot field. The calculated slot admittance has good accuracy when compared with measurements on a chosen geometry View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of coplanar waveguide-fed microstrip antennas

    Page(s): 734 - 737
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    A moment method analysis of a microstrip antenna fed by an open-end coplanar waveguide is presented. The surface electric current on the microstrip antenna is represented by the entire domain basis functions, while the surface magnetic currents in the open-end slot and in the slots of the coplanar waveguide near the open end are expanded by the subsectional roof-top basis functions. Some practical numerical aspects are carefully discussed, and a numerical device is introduced to reduce the computation time for the integrals involving roof-top basis functions and the spectral-domain Green's function. The solution accuracy is thus improved. Computed results for the reflection coefficients and input impedances are given and compared with measured values. Good agreement between theory and experiment is obtained View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Incremental diffraction coefficients for the extended physical theory of diffraction

    Page(s): 732 - 734
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    The extended physical theory of diffraction (EPTD), which is an extension of Ufimtsev's (1962) theory to aperture integration, is formulated in terms of incremental diffraction coefficients (IDC). Closed-form expressions for these coefficients are derived. The utility of the derived IDC is exemplified in a calculation of the cross-polar pattern of a parabolic reflector View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A failure of a numerical electromagnetics code to match a simple boundary condition

    Page(s): 723 - 727
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    It is shown that it is impossible to satisfy the boundary condition for a perfectly conducting hemisphere-capped dipole without creating a discontinuity in the first derivative of the scattered field on the boundary. Since solutions of Maxwell's equations are analytic in a source-free region, all field derivatives must be continuous in the region where the source-free equations are satisfied. The basis functions used by the generalized multipole technique (GMT) are solutions of Maxwell's source-free equations in a region which includes the scattering surface. Therefore, a GMT solution to the dipole problem can exist only in the sense that the boundary value error approaches zero as the number of basis functions approaches infinity. This in itself is not surprising, but the difficulty of matching the boundary condition at the discontinuity affects the convergence of the technique. For the method-of-moments (MOM) technique, where a source current exists on the scattering surface, it is not clear if a perfect boundary value solution to the dipole problem can be theoretically realized or not 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