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Antennas and Propagation, IEEE Transactions on

Issue 6 • Date June 1993

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Displaying Results 1 - 22 of 22
  • An alternative version of the time-domain electric field integral equation for arbitrarily shaped conductors

    Publication Year: 1993 , Page(s): 831 - 834
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB)  

    An alternative version of the time-domain electric field integral equation for arbitrarily shaped conducting structures is presented. The advantage of the present approach is that the electric field integral equation has one less derivative with respect to time than the popularly used one. Hence, with this approach one does not need to differentiate the excitation. Therefore impulse and step function excitations of the conducting structures are possible in addition to the conventionally used Gaussian excitations. This alternative version is also quite accurate compared with a frequency-domain solution.<> View full abstract»

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  • A numerical study of a dielectric disk antenna above grounded dielectric substrate

    Publication Year: 1993 , Page(s): 813 - 821
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    An antenna made of a dielectric disk with a high permittivity mounted on top of a grounded dielectric substrate of low permittivity is analyzed. A numerical procedure based on surface integral equations, derived from the equivalence principle, is used to compute the natural resonant frequencies for the HEM11 mode from which the radiation Q factor of the antenna is obtained. Then the radiation pattern of the antenna, operating at the resonant frequency evaluated previously, is computed with an electric dipole excitation located within the dielectric substrate under the dielectric disk. The effect of various parameters on the radiation characteristics of the antenna is studied, and presented in the form of diagrams. The low values of the radiation Q, combined with the high values of the dielectric Q and conductor Q, indicate that this antenna promises to be more efficient then the microstrip antenna View full abstract»

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  • Spectral analysis and synthesis options for short pulse radiation from a point dipole in a grounded dielectric layer

    Publication Year: 1993 , Page(s): 747 - 754
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    Formal exact alternative spectral representations for the electromagnetic fields radiation from a pulsed electric current element embedded in a grounded dielectric layer are derived. Starting from the standard spectral decomposition into the real frequency domain and the real spatial wavenumber domains corresponding to the transverse coordinates perpendicular to the direction of stratification, alternative treatments of the spectral integrands in the various complex spectral planes lead to exact steepest descent path representations which are well suited for subsequent asymptotic reduction into the time domain (TD). Of special interest is the nonconventional synthesis strategy, which performs frequency inversion before spatial wavenumber inversion, thereby utilizing in one of the options TD leaky modes with complex frequency and real spatial wavenumbers, and also TD trapped modes, as basis fields. This is contrasted with the conventional approach built around time-harmonic real-frequency leaky modes with complex spatial spectra. The spectral strategies employed here are applicable also to layered structures View full abstract»

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  • Subarray-synthesized low-side-lobe sum and difference patterns with partial common weights

    Publication Year: 1993 , Page(s): 791 - 800
    Cited by:  Papers (5)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    Methods of synthesizing low-side-lobe sum and difference patterns for linear arrays are described. By subarray beam forming, the sum and difference patterns exhibit a common factor, leading to a simple monopulse estimator. A procedure is proposed for the synthesis of the subarray-based sum and difference patterns which approximate a set of reference patterns in least-squares sense. Supervised nulling is incorporated as a means of suppression of strong interference. To further reduce system complexity, the constraint that parts of the beam-forming weights are shared by the sum and difference channels is imposed. The relationship between the maximum number of common weights allowable and the number of subarrays used is discussed. Numerical results are presented to demonstrate the efficacy of the proposed methods View full abstract»

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  • Microscale diversity in satellite communications

    Publication Year: 1993 , Page(s): 801 - 805
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Results from an investigation into a microscale diversity scheme for the purpose of mitigating attenuation due to tropospheric scintillations are presented. Data from an experiment using the 20-GHz Olympus satellite beacon were analyzed to evaluate the performance of short-baseline site-diversity systems. Results indicate that with a baseline separation of about 50 m (at an elevation angle of 14° in this experiment) the signals received by the main and diversity terminals become decorrelated. Examination of several high-scintillation events shows that such a diversity technique could substantially increase the uptime of low-power-margin VSAT systems. The performance of microscale diversity for several baseline separations is evaluated in terms of a parameter called diversity recovery. Applications and conditions under which microscale diversity performs best are addressed View full abstract»

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  • Mechanisms governing propagation between different floors in buildings

    Publication Year: 1993 , Page(s): 787 - 790
    Cited by:  Papers (49)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The potential implementation of wireless radio local area networks (LANs) and personal communication services inside buildings requires a thorough understanding of signal propagation within buildings. In this work the authors develop a theory which explains propagation between a transmitter and a receiver located on different floors of a building. Depending on the structure of the building and the location of the antennas, either direct ray propagation through floors or diffraction outside the building will determine the propagation characteristics and range dependence of the signal sector average as the number of floors between the transmitter and the receiver is increased View full abstract»

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  • Effects of a resistively coated dielectric strip on the TM-polarized resonant backscatter behavior of a slotted conducting rectangular shell

    Publication Year: 1993 , Page(s): 834 - 837
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    The performance of a resistively coated dielectric strip used to suppress the first TM-type resonant backscatter associated with a two-dimensional slotted conducting rectangular shell is analyzed using the moment method technique. Results obtained indicate that almost perfect resonance damping performances are attained when a finite-sized strip with dielectric constants ∈r=4-j0.4 and film resistance Rs=188.5 Ω is placed: (1) at the slot (which directly faces the normally incident TM-polarized plane wave), (2) on the interior perimeter of the shell adjacent to the slot, or (3) at the center of the back wall of the shell. Poorer damping performances are observed, however, with the strip placed at other positions and/or with the same or higher film resistance. It is also shown that in general the knowledge of waveguide theory can be used advantageously in the placement of the strip for achieving best resonance damping performance View full abstract»

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  • On the radiation of horn clusters including mutual coupling and the effects of finite metal plates: application to the synthesis of contoured beam antennas

    Publication Year: 1993 , Page(s): 713 - 722
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    This work describes a model of the radiation of horn clusters for contoured beam antennas. The model includes internal mutual coupling (through a power divider network), modal conversions and reflections inside the horns, external mutual coupling and the effects of the edges of the metal plate that holds the cluster together. This model is applied to the synthesis of the direct broadcast satellite (DBS) antenna of the HISPASAT satellite, the computed immersed patterns of each horn being used in the optimization of the excitations. Results are given concerning model validation and optimization with immersed patterns View full abstract»

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  • A new low-side-lobe pattern synthesis technique for conformal arrays

    Publication Year: 1993 , Page(s): 824 - 831
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    The application of the new nonlinear optimization algorithms to array design is demonstrated by the low-side-lobe pattern synthesis of conformal arrays. By adopting the information of array element realized gain patterns the authors formulate synthesis problems as nonlinearly constrained optimization problems, and propose a direct method to solve them. The technique allows them to find a set of array coefficients that yield a pattern meeting a specified side-lobe level and achieving the maximum directivity, if such a set of array coefficients exists. If the side-lobe specifications cannot be met with the given array, the technique will result in a set of coefficients that yield a pattern meeting the best attainable side-lobe level and having directivity as high as possible. Simplified synthesis problems for an axial dipole array in an infinite, perfectly conducting cylinder are discussed, and numerical results are given. The synthesis technique works for general array patterns View full abstract»

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  • Asymptotic analysis and numerical evaluation of short pulse radiation from a point dipole in a grounded dielectric layer

    Publication Year: 1993 , Page(s): 762 - 769
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    In a companion paper (see ibid., p.747-54, Jun 1993) spectral options for the synthesis of the electromagnetic fields radiated into the exterior by a pulsed electric current element inside a grounded dielectric layer are presented. The exact spectral integrals, which implement these spectral alternatives, are reduced here by asymptotic methods that extract explicit approximate forms for wavefront contributions, time-domain (TD) leaky mode contributions with space-time dependent wavenumbers and frequencies, and self-consistent hybrid combinations of both. The resulting hybrid wavefront-TD-leaky-mode algorithm is explained in physical terms and tested numerically. For both TE and TM contributions, it is found that in their domain of validity, the TD leaky modes excited within the frequency spectrum of the source pulse synthesize with remarkable accuracy the highly resolved pulse train obtained by direct tracking of multiple reflected wavefronts. Of special interest is the anomalous behavior of the TM-TD leaky modes when their angular spectra are near the Brewster angle for the air-dielectric interface. The correspondingly anomalous asymptotics is explained in detail View full abstract»

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  • A simple and accurate complex image interpretation of vertical antennas present in contiguous dielectric half-spaces

    Publication Year: 1993 , Page(s): 806 - 812
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    An efficient technique is developed to solve the important problem of vertical antennas located above and penetrating the interface between contiguous dielectric half-spaces. It begins by deriving the spectral expressions of the vector and scalar potential Green functions in terms of the TM wave spectral transmission coefficient. The complex image technique is used to derive simple, accurate, and rapidly convergent expressions of the full-wave spatial Green functions. The spatial Green functions are used in the moment method to model vertical thin-wire antennas residing above the penetrating the interface separating the contiguous dielectric half-spaces with and without loss View full abstract»

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  • Effects on portable antennas of the presence of a person

    Publication Year: 1993 , Page(s): 739 - 746
    Cited by:  Papers (102)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    This work deals with the influence the presence of a person has on the performance of antennas for hand-held portable telephones. It is shown how input impedance, far-field radiation pattern, radiation efficiency, and the magnitude of the near field are affected by the presence of the human body. The investigations have been carried out by applying the finite-difference time-domain (FDTD) technique to a model of the telephone with a λ/4 monopole antenna and a simple hand-head model of the operator. Results from this configuration are compared with results for the telephone box and antenna alone. Measurements have been performed to verify the results obtained by simulations. The results show that a shadow effect in the far-field pattern occurs in the direction of the person and that the radiation pattern, including polarization, changes considerably from the telephone with the antenna alone. The impedance results show a change in resonance frequency when the telephone is placed next to a person. Results for radiation efficiency show that close to half of the energy is absorbed by hand and head. On average a system loss of 3-4 dB should be included in a link budget, and there is considerable fading, even in a radio-anechoic chamber, when persons move around in a natural manner View full abstract»

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  • Polynomial characterization of inhomogeneous media and their reconstruction using an open-ended waveguide

    Publication Year: 1993 , Page(s): 822 - 824
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    B. Sanadiki and M. Moustafavi (1991) described how an inhomogeneous continuously varying dielectric profile can be inverted using a stepwise successive refinement procedure when an open-ended waveguide is used as the source. Here, an alternative approach based on polynomial characterization of the dielectric medium is discussed. It is shown that this method is more efficient and avoids the convergence difficulties of the previous method for most cases except for discontinuous or stratified profiles View full abstract»

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  • Scattering by S-shaped surfaces

    Publication Year: 1993 , Page(s): 701 - 708
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    When an S-shaped surface possesses no derivative discontinuities, techniques such as the geometrical theory of diffraction are not applicable. However, if the radius of curvature is relatively large at every point on the surface, the physical optics approximation may be employed. The authors present a uniform physical optics (UPO) solution which remains valid at caustics occurring when two or more specular points coalesce at the inflection point of the S-shaped surface. The solution is developed by approximating the surface with a localized cubic expansion, leading to exact expressions in terms of Airy integrals. In contrast to other solutions, the one given here requires only a knowledge of the stationary phase points and the first three derivatives of the surface-generating function at those points. A major effort is devoted to the validation of the UPO solution, and this is accomplished with numerical models of the S-shaped surface. It is found that the given UPO solution is quite accurate in the specular and nonspecular regions View full abstract»

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  • Design of scanning spherical trireflector antennas with high aperture efficiency

    Publication Year: 1993 , Page(s): 778 - 786
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB)  

    It is frequently desirable to scan the main beam of a large antenna system without moving the main aperture structure. Spherical reflectors have excellent potential in this application. However, they are not commonly used because of poor aperture efficiency and high side lobes in traditional implementations. This work introduces a new dual-subreflector feed system design which does not require oversizing the spherical main reflector to accommodate scan and yet permits a controlled aperture illumination. The design yields high aperture efficiency, low cross-polarization, and low side lobes View full abstract»

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  • E-plane scan performance of infinite arrays of dipoles printed on protruding dielectric substrates: coplanar feed line and E-plane metallic wall effects

    Publication Year: 1993 , Page(s): 837 - 841
    Cited by:  Papers (10)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    The effects of coplanar feed lines and of E-plane cavity walls on the performance of infinite arrays of dipoles printed on protruding dielectric substrates are investigated. In order to do so, two unit cell configurations are studied: (1) the dipole element fed by coplanar transmission lines and (2) the dipole element fed by coplanar transmission lines with finite-height metallic walls added parallel to the H-plane of the array. The element active impedances are calculated for these configurations, and they are compared with those obtained from arrays of dipoles without coplanar feed lines. Effects of the dielectric substrate permittivity and of its thickness on the array element active impedance are included. The results show that the arrays of dipoles with the coplanar feed lines exhibit feed-line-induced blindnesses which reduce considerably the scan volume of the array. It is also shown that these feed line effects are reduced for thicker or higher permittivity substrates, and that the insertion of electric walls is one possible avenue for eliminating these anomalies View full abstract»

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  • Time-domain leaky modes on layered media: dispersion characteristics and synthesis of pulsed radiation

    Publication Year: 1993 , Page(s): 755 - 761
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    In a companion paper (see ibid., p.747-54, June 1993) studying short-pulse radiation from current elements in the presence of plane layered dielectric media, various alternatives for constructing the transient field in terms of spectral-domain wave functions are explored. Two distinctive synthesis options are structured around conventional time-harmonic and nonconventional time-dependent basis wave functions, respectively. To understand the characteristic properties of each, the frequency-wavenumber dispersion relation for the layered environment is explored here in detail. Especially interesting is the behavior of the nonconventional time-domain leaky modes, which exhibit anomalies not encountered in their conventional time-harmonic counterparts. An example is given of how these time-domain modal basis fields synthesize highly resolved short-pulse radiation from a source in a dielectric layer View full abstract»

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  • Analysis of electromagnetic scattering from doubly periodic nonplanar surfaces using a patch-current model

    Publication Year: 1993 , Page(s): 732 - 738
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    A solution is presented for the problem of scattering of a time-harmonic plane wave from a surface separating two contrasting homogeneous media. The reflected and the transmitted fields are approximated by a linear combination of the fields due to sets of fictitious patch sources supporting surface currents of cross-polarization. Spatially periodic and properly modulated, these fictitious sources lie at some distance from the physical surface, each in a plane parallel to the directions of the periodicity. The fields radiated by these patch sources are computed by summing a spectrum of Floquet modes. The complex amplitudes of these fictitious sources are adjusted simultaneously to render the tangential components of the electric and magnetic fields continuous at a selected set of points on the surface. The suggested procedure is simple to implement and is applicable to arbitrary, smooth, doubly periodic surfaces. The accuracy of the method has been demonstrated for doubly periodic sinusoidal surfaces. Perfectly conducting surfaces have also been treated within the general procedure as a reduced case View full abstract»

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  • Electromagnetic scattering from an arbitrary, inhomogeneous 2-D object-a finite and infinite element solution

    Publication Year: 1993 , Page(s): 770 - 777
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    The application of finite elements to the open region associated with scattering problems necessarily requires the truncation of the solution region. This work investigates the use of infinite elements to extend the solution region beyond that of the finite elements which can be truncated by a noncircular boundary. A finite/infinite element formulated is developed in two dimensions and tested on dielectric, magnetic, and conducting scatterers with known analytic solutions View full abstract»

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  • A two-year measurement of rainfall attenuation of CW microwaves in Singapore

    Publication Year: 1993 , Page(s): 709 - 712
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    The authors present two-year statistics on the rainfall attenuation of 21.225 GHz vertically polarized CW microwave signals in Singapore. The CCIR recommendation is found to underestimate the microwave specific attenuation (dB/km) per path average rain rate (mm/h) as well as the accumulated time of attenuation exceeding preset levels. A negative exponential raindrop size distribution based on spherical droplets is constructed from the measured data View full abstract»

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  • Enhanced electromagnetic power deposition in a lossy medium

    Publication Year: 1993 , Page(s): 723 - 726
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    It is demonstrated that an aperture antenna, excited by a leaky wave, will transfer power into an homogeneous lossy half-space at levels exceeding expectation. However, such local enhancements are only possible in the near-field region in the central part of the array. With the proper choice of parameters, enhancements of the order of 15 dB can be achieved. The calculated results are relevant to hyperthermic heating in cancer therapy and to related problems in biological hazards View full abstract»

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  • Space and time wave shaping for transmission into a lossy medium

    Publication Year: 1993 , Page(s): 727 - 731
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    Electromagnetic waves traveling into a lossy medium suffer distortion in both time and space. This situation poses a design problem if it is desired to have a specified form, in both time and space, for the fields at a given location in the lossy medium. An analytical procedure is presented so that the specified field in a lossy conducting half-space can be realized with a discrete array of concentric loop currents on the surface. Each loop current is stepped on at a finite sequence of discrete times. The procedure could be applied in geophysical subsurface probing, hyperthermic cancer therapy, and digital signal transmission 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