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Antennas and Propagation, IEEE Transactions on

Issue 4 • Date April 1994

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Displaying Results 1 - 25 of 26
  • Planar near-field to far-field transformation using an array of dipole probes

    Page(s): 534 - 537
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    A method is presented for computing far-field antenna patterns from measured near-field data measured by an array of planar dipole probes. The method utilizes the near-field data to determine some equivalent magnetic current sources over a fictitious planar surface which encompasses the antenna. These currents are then used to find the far fields. The near-field measurement is carried out by terminating each dipole with 50 /spl Omega/ load impedances and measuring the complex voltages across the loads. An electric field integral equation (EFIE) is developed to relate the measured complex voltages to the equivalent magnetic currents. The mutual coupling between the array of probes and the test antenna modeled by magnetic dipoles is taken into account. The method of moments with Galerkin's type solution procedure is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient-fast Fourier transformation (CG-FFT) method exploiting the block Toeplitz structure of the matrix. Numerical results are presented for several antenna configurations to show the validity of the method.<> View full abstract»

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  • Comments on "Radiation and scattering from thin wires in chiral media"

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (86 KB)  

    Comments that the above paper (see Jaggard, Liu, Grot and Pelet, IEEE Trans. Antennas Propagat., vol.40, p.1273-1282, Nov. 1992) lacks the generality of the paper published by Monzon (see Antennas Propagat., vol.38, p.227-235, Feb. 1990). The latter paper contains an analysis for thin wires, including an explicit integral equation and method for numerical solution (summing impedance matrices), which renders the problem of trivial numerical implementation. Further, the analysis applies to full biisotropic regions, and is therefore more general than chiral since chiral is just a special case of biisotropic. It appears that Jaggard et. al. use the integral equation of Monzon and follow the numerical scheme therein literally.<> View full abstract»

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  • Predictions of radiowave attenuations due to a melting layer of precipitation

    Page(s): 492 - 500
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    A melting layer model related to the physical constants and meteorological parameters is employed in this investigation. The specific phase shift, together with the specific attenuation, is computed at 1-100 GHz by using the Mie theory. The additional zenith attenuation, which is the difference between zenith attenuation due to the melting layer and attenuation due to the same thickness of the resulting rain, is comprehensively studied. The ratio of the difference to rain zenith attenuation may be over 1 at 1-5 GHz although the difference is much less than 1 dB. The difference can be over 1 dB at frequencies above 20 GHz. A minimum of the ratio is below 0.05 at frequencies about 40-60 GHz but the ratio can become a value of about 0.1 at 100 GHz. The additional attenuation should be taken into account in satellite-Earth communications and radar remote sensing. The power law parameters of the average specific attenuation of the melting layer and rain specific attenuation are tabulated for three raindrop size distributions at rain rates of below 25 mm/h. The power law method could be utilized in the additional attenuation calculation. It is a good approximation of the Mie theory results at 1-50 GHz and a useful estimate at 50-100 GHz View full abstract»

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  • Error analysis for far-field approximate expression of Sommerfeld-type integral

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    The error of the Sommerfeld-type integral approximate expression given by Chew (1988) in the far field is discussed. It is demonstrated that Chew's method is correct, not only intuitively, but also rigorously View full abstract»

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  • Scattering from perfectly conducting and resistive strips on a grounded dielectric slab

    Page(s): 552 - 556
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    The scattering properties of perfectly conducting and resistive strips are predicted for strips which are located on a dielectric slab backed by a perfectly conducting ground plane. The spectral domain Green's function is used to relate the currents and fields on the strip, and the resulting integral equation is solved using the method of moments. Both TE and TM strips are examined using piecewise linear and pulse subdomain basis functions, respectively, to model the current on the strip. Calculated results are compared with results measured at the NASA Langley Research Center View full abstract»

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  • Electromagnetic backscattering from a helicopter rotor in the decametric wave band regime

    Page(s): 501 - 509
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    The paper gives a theoretical solution to the problem of determining the radar cross section and Doppler spectrum of a helicopter rotor as presented to a radar operating in the decametric wave band (3-30 MHz). At such frequencies for all practical rotors the scattering regime is either Rayleighan or resonant. The solution proceeds by modeling the rotor as an equivalent set of radial wires on which the incident wave is assumed to excite sinusoidally distributed currents. It is shown that, subject to certain simplifying assumptions, the Doppler spectrum has a form similar to that associated with tone modulation of a frequency modulated bearer. The theoretical work is confirmed by experiment View full abstract»

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  • A technique for measuring antenna drive port impedance using backscatter data

    Page(s): 526 - 533
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    This paper describes a technique for measuring the drive port impedance, denoted ZD, of an antenna using radar backscatter data. It requires only that one has access to the antenna terminal ports, and the ability to attach a known load to the terminals. In the technique described here, three sets of backscatter data (amplitude and phase) are required: one with the terminals short-circuited, denoted E s, one with the terminals open-circuited, denoted Eo , and the third with the terminals loaded with a known resistance Ro, denoted E1. These data are readily processed to obtain ZD, according to the simple relationship defined in equation (8). An analysis of the effects of the various error sources affecting the value of ZD determined using this technique is also presented. The utility of the technique is illustrated by measuring ZD for a “canonical” body using measured results at L band and UHF taken on three differing RCS ranges, selected so that they differ in the quality of the backscatter measurement over the frequency range under consideration View full abstract»

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  • Human operator coupling effects on radiation characteristics of a portable communication dipole antenna

    Page(s): 556 - 560
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    EM coupling effects of a human operator on antenna radiation characteristics, such as the antenna input impedance, radiation patterns, the radiation power (into free space), the power absorbed by the body, the radiation efficiency, etc., of a portable communication dipole antenna were investigated in detail. A realistically shaped 3D man model and an approximate linear dipole antenna were used to model this problem. Coupled integral equations (CIE) and the method of moments (MoM) were employed to numerically solve this antenna-body coupling problem. Numerical examples are presented for the antenna located in front of the head (distance ranging from 5 to 1 cm) or adjacent to the abdomen (0.6 cm distance) at 830 MHz. It is found that, when coupled with the operator body, the antenna input impedance will have significant deviation from those in free space and different positions. Due to the operator body absorption effect, the maximum attenuation of the H-plane antenna gain may reach about 15 dB for the antenna at the head position and 25 dB for the abdomen position, toward the direction of the body side. Also, the antenna radiation efficiency is reduced to the range from 0.72 to 0.29 for the head position and 0.15 for the abdomen position, respectively. Moreover, the cross-polarization field is significant, especially in the E plane of φ=90°. This is important for the antenna RF design and communication link budget consideration of portable radio systems View full abstract»

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  • A magnetic current loop array in a reflector antenna

    Page(s): 575 - 576
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    A magnetic current loop antenna array is designed, implemented, and measured. Radiation pattern, input impedance, and efficiency of the array are presented. The array is intended as a feed in a reflector antenna. Using a 360 mm solid dish, the overall gain of the reflector antenna is 24.6 dB at 9 GHz. The tolerance in placing the feed at the focal point of the dish is high. The present feed is low cost, self-supportive, robust, and easy to manufacture. It is an ideal substitute for the horn in a TVRO or VSAT antenna View full abstract»

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  • SEM representation of the early and late time fields scattered from wire targets

    Page(s): 564 - 566
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    In the communication, the singularity expansion method (SEM) is used to express the field scattered from an arbitrary thin-wire target. Explicit expressions are given for both the class-1 and class-2 representations of the scattered field due to step excitations. Numerical results are given for the early-time transient fields scattered from both a straight wire and a simple swept-wing aircraft model. The results of the SEM computations are compared to fields obtained by Fourier inversion techniques. It is shown that the class-2 representation yields a significant improvement over the class-1 result during the early-time interval, albeit at the expense of a more complex computation View full abstract»

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  • A shaped single reflector offset antenna with low cross-polarization fed by a lens horn

    Page(s): 478 - 483
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    A novel compact primary-fed offset reflector antenna with the potential of radiating circular as well as elliptical beams with low cross-polarization, is proposed. The reflector is fed by a horn with a phase-correcting lens in the aperture. Compared to the dual-reflector offset antenna, the concept is easier to assemble and mechanically more robust. The antenna has been synthesized and analyzed by computer programs resulting from modifications of corresponding PO programs for dual-reflector offset antennas. The synthesized antenna exhibits similar cross-polarization, side-lobe level, and aperture efficiency as those of dual-reflector offset antennas, although the one-to-one correspondence between zero cross-polarization and conformal mapping from the feed to the aperture, is not exactly valid for this approach View full abstract»

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  • Response to “Comments on `Radiation and scattering from thin wires in chiral media'”

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB)  

    Replies that Monzon appears to imply that Jaggard, Liu, Grot and Pelet (see IEEE Trans. Antennas Propagat., vol.40, p.1273-1282, 1992) paper was not completely independent of his published work (see Monzon, IEEE Trans. Antennas Propagat., vol.38, p. 227-235, 1990). A brief chronology of the documented research effort is given to clear any misunderstanding. An abstract of Jaggard et. al. works displayed wire currents which could have only come from numerically solving the chiral integral equation in question. Since they did not have access to Monzon's paper before its publication it is impossible for their research to have used the results of Monzon. What appears to have happened is that two different groups discovered the chiral version of Pocklington's integral equation coincidentally and independently View full abstract»

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  • The scattering properties of “Super Dense” arrays of dipoles

    Page(s): 463 - 472
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    This paper deals with a new class of dichroic surfaces that are capable of extremely broadbanded reflection properties (from an octave to a decade bandwidth) while being transparent at lower frequencies. It is obtained by having the effective interelement spacing reduced to a very small value without reducing the element size. While such surfaces, referred to as “Super Dense” surfaces, can be implemented in a number of ways, this paper addresses the most fundamental type, namely the type made up of two orthogonal arrays of densely packed wire elements (“dipoles”) arranged in a square grid, and placed almost, but not quite in the same plane. The two orthogonal arrays allow the surface to handle arbitrary polarizations View full abstract»

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  • The reciprocity and power conservation principles for boundary conditions on a semitransparent surface

    Page(s): 449 - 452
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    Generalized boundary conditions of coupling on a semitransparent surface are valid only if the Lorentz reciprocity theorem and the electromagnetic power conservation principle are satisfied on the surface with these boundary conditions. These criteria are reformulated as relations between the tensors in the boundary conditions. Some known boundary conditions of coupling are considered View full abstract»

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  • Resonance properties of dielectric waveguide gratings: theory and experiments at 4-18 GHz

    Page(s): 567 - 569
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    The guided-mode resonance characteristics of dielectric waveguide gratings are presented. The sharp resonance features predicted theoretically are experimentally observed in the microwave region (4-18 GHz) and are shown to be in agreement with theory View full abstract»

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  • Full-wave solution for an aperture-coupled patch fed by perpendicular coplanar strips

    Page(s): 544 - 547
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    In recent years, the rectangular slot has been proposed as a means of power transfer between layers in multilayer printed antennas. Compared to probes, slots reduce fabrication complexity considerably, and allow more flexibility in the design of multilayer configurations. In the past, the aperture-coupled microstrip patch has been analyzed using the reciprocity theorem for the feeding line and the method of moments for the patch. The same method is used here for the analysis of an aperture-coupled patch fed by perpendicular coplanar strips. Theoretical results from this solution are compared with measurements for the input impedance of this antenna, and design data are given for the characteristic impedance of the coplanar strip feed line View full abstract»

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  • Certain considerations in aperture synthesis of ultrawideband/short-pulse radiation

    Page(s): 518 - 525
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    The authors consider certain characteristics of the radiation from collimated, ultrawideband short-pulse aperture distributions. It is shown that an efficient radiation must account for the multifrequency nature of the field. Two alternative schemes for wideband aperture synthesis of an impulse-like radiation pattern are examined. The first, entitled the “iso-width aperture”, utilizes only temporal shaping of the excitation pulse. In the other, the “iso-diffracting aperture”, they suggest source shaping in space-time so that all the frequency components in the field have the same collimation distance. The “iso-diffracting” scheme yields higher directivity and more efficient pulsed radiation. Explicit examples for the pulsed source distribution and for the pulsed radiation patterns are presented, parametrized, and contrasted View full abstract»

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  • Perturbation technique for matrix equations and its application in the computation of internal fields in a three-dimensional arbitrarily shaped biological body

    Page(s): 569 - 573
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    A novel matrix perturbation technique for the matrix equation [A][u]=[b] is presented. One of its applications, the computation of internal fields in a three-dimensional arbitrarily shaped heterogeneous biological body illuminated by a plane wave, is further investigated by using the technique. If one regards a normal biological body as the primary model and stores its computation results, when small perturbations in the dielectric characteristics or the shape of the body occur, the internal fields in the perturbed biological body can be rapidly computed using the stored results. Compared with the usual moment methods, the new technique has an equivalent precision, yet takes only 1/70 the execution time. This technique is especially suitable for pathological cases in which the dielectric characteristics or the shape of the biological body vary due to disease View full abstract»

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  • Electromagnetic scattering from two adjacent objects

    Page(s): 510 - 517
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    In the paper, the problem of electromagnetic scattering from two adjacent particles is considered and an iterative solution that accounts for multiple scattering up to second-order is proposed. The first-order solution can easily be obtained by calculating the scattered field of isolated particles when illuminated by a plane-wave. To get the second-order solution, the scattered field from one of the particles, with nonuniform phase, amplitude, and polarization, is considered as the illuminating wave for the other particle and vice versa. In the work, the second-order scattered field is derived analytically using a novel technique based on the reciprocity theorem. In specific, the analytical solution for bistatic specular scattering from a cylinder and sphere pair is discussed and the results are compared with numerical computations based on the method of moments View full abstract»

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  • Transient interactions of an EM pulse with a dielectric spherical shell

    Page(s): 453 - 462
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    The authors study the scattering interaction of short electromagnetic pulses with a spherical target. The target is assumed penetrable and they model it as an air-filled dielectric shell. The radar cross-section (RCS) of such a target is obtained and its resonance features are analyzed. A dielectric composition makes the resonance features become very prominent compared with the case of a perfectly conducting sphere. When the interrogating waveform is a pulse of short duration, the resonance features of the RCS can be extracted within the frequency band of the spectrum of the incident pulse. To verify their theoretical predictions they illuminate spherical targets with short, broadband pulses using an impulse radar system. The actual shape of the pulse that is incident on the targets is theoretically modeled using a digital filter design technique together with pulse returns from a reference target. They verify that the shape of the predicted, backscattered pulse that results from their design method agrees well with the experimental findings using three additional targets of different sizes and materials. They investigate in the combined time-frequency domain the development in time of the various frequency features of the spectra of backscattered pulses using time-windowed Fourier transforms. The methodology developed can handle broadband pulses of any sufficiently smooth spectrum, interacting with (lossy or lossless) dielectric scatterers, and can extract resonance features within the frequency band of the spectrum of the transmitted pulse. Accordingly, this method could be also used for assessing the performance of high-power impulse radar systems View full abstract»

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  • Some computational aspects of Pocklington's electric field integral equation for thin wires

    Page(s): 561 - 563
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    A procedure is presented for extracting the singularity from the kernel in Pocklington's electric field integral equation for thin wires. The modified kernel which results may be used to dramatically improve the computational efficiency of certain moment method formulations. A simple example is considered in which pulse basis functions and point matching are used. For this case, a convenient approximation of the self-impedance term is also derived View full abstract»

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  • Integral equation analysis of a sheet impedance coated window slot antenna

    Page(s): 541 - 544
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    Presents an integral equation and method of moments analysis of a window slot antenna. The antenna is modeled by a sheet admittance coated rectangular aperture in an infinite ground plane. It is shown that the sheet admittance coated aperture is complementary to a sheet impedance plate, which permits the window slot antenna to be analyzed with existing computer programs. Numerical results are compared with measurements for input impedance and radiation efficiency View full abstract»

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  • A design of AM/FM mobile telephone triband antenna

    Page(s): 538 - 540
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    In vehicles, antennas for AM/FM broadcasting (BC) and cellular mobile telephone (MT) are usually mounted on the car's body. However, a triband antenna which can be used for both AM/FM BC and MT is more desirable to decrease the number of antennas. An outline of the general design for the AM/FM MT triband antenna with coils is described. Next, the design of a new triband antenna with double sleeves instead of coils is presented. The double sleeves consist of two coaxial lines connected in series. It is shown that the triband antenna with double sleeves has good characteristics, including radiation patterns and voltage standing-wave ratio (VSWR) View full abstract»

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  • Sectoral pattern synthesis with primary feeds

    Page(s): 484 - 491
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    This paper presents investigations carried out at CNET in order to design a primary feed radiating a sectoral pattern (±70°). A rough synthesis method based on the equivalent radiating aperture of the feed is first used. Then it rigorously studies the electromagnetic performances of many related structures with a highly accurate analysis software based on the integral equation formulation. Lastly, it selects the final design for the feed horn and presents two breadboards and the associated measurements (normalized impedance and far field patterns) which show excellent agreement with simulation View full abstract»

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  • The far-field of a spherical array of point dipoles

    Page(s): 473 - 477
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    In this paper, the far-field of a spherical array of point dipoles is related to the array currents in an elegant manner by invoking the properties of the associated Legendre functions. The inverse problem, viz., determining the array currents from the far-field data is solved in a recursive manner thereby precluding the need for a matrix inversion 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