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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 1 • Date Feb 1994

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Displaying Results 1 - 10 of 10
  • Analysis of a dielectric resonator antenna in a cylindrical conducting cavity: HEM modes

    Page(s): 8 - 14
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    Numerical modelling has been performed for the hybrid HEM modes of a flush-mounted dielectric resonator antenna in a cylindrical conducting cavity. The antenna is formed by a conducting cavity with a dielectric post and radiates through an annular slot in the upper ground plane. Coupled aperture magnetic current integral equations are used to model the slot and the effect of the post resonator and the cavity are included via Green's function techniques. The moment method is applied to the coupled integral equations and the complex resonant frequencies for the antenna structure are found by searching for the zeros of the determinant of the impedance matrix in the complex frequency plane. The radiation Q factor, slot field distribution and radiation field are subsequently computed at the resonant frequency. The HEM modes with the lowest resonant frequencies have been investigated for different geometrical configurations View full abstract»

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  • Broadband design of coaxial line/rectangular waveguide probe transition

    Page(s): 53 - 58
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    A theoretical model is presented for a coaxial-line probe to rectangular-waveguide transition for the case where the probe is dielectrically sheathed and extends part of the way into the waveguide. Comparison of theoretical with experimental results demonstrates that the model is very accurate. The model is used to perform a bandwidth investigation of both sheathed and unsheathed probe transitions to gain insight into the effects of various junction parameters. It is found that the electrical size of the coaxial-line aperture in the waveguide plays a significant role in the overall bandwidth performance of the transition, and in many cases the bandwidth performance may be enhanced by offsetting the location of the junction from the centre of the waveguide or by dielectrically sheathing the probe in the waveguide View full abstract»

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  • Taking into account the edge condition in the problem of scattering from the circular aperture in circular-to-rectangular and rectangular-to-rectangular waveguide junctions

    Page(s): 45 - 51
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    An integral equation for the equivalent magnetic current sheet at the centred circular aperture of a diaphragm in a transverse plane of circular-to-rectangular and rectangular-to-rectangular waveguide junctions is approximately solved by Galerkin's method. A basis of weighted Jacobi polynomials which satisfy the edge condition is used for the magnetic current. The results are graphically compared with formulas derived from the variational theory given in the Waveguide Handbook (McGraw Hill, New York, 1951) View full abstract»

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  • Precision of radio reflector surfaces adjusted from theodolite-tape measurements

    Page(s): 23 - 29
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    The authors analyse the surface errors of five reflectors of millimetre and centimetre wavelength radiotelescopes which were initially adjusted from theodolite-tape measurements. The initial adjustment of the millimetre-wavelength reflectors was later measured more precisely by radio holography. All reflectors had systematic ring-like zone deviations and superimposed random deviations of Gaussian distribution of which the dispersion increases towards the reflector rim. Such spatially nonuniform surface errors are typical for adjustments from theodolite-tape measurements View full abstract»

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  • Accurate absorbing boundary conditions for the FDTD analysis of H-plane waveguide discontinuities

    Page(s): 59 - 61
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A brief discussion about absorbing boundary conditions is presented which focuses on the FDTD modelling of waveguide discontinuities. An accurate first-order ABC is developed and tested, and also second-order ABCs are designed and discussed, which are used with a nonmonochromatic excitation. Finally, these ABCs are used in the study of some common H-plane waveguide discontinuities: a waveguide-type dielectric filter and an open-ended flanged parallel plate waveguide View full abstract»

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  • Survey of analytical and numerical models for probe-fed microstrip antennas

    Page(s): 15 - 22
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    An abundant literature on the theoretical and experimental investigation of probe-fed microstrip antennas has been published in recent years. The models presented are generally valid for small values of H/λ0. The authors give a historical survey of the analytical and numerical models for this type of antenna and propose a numerical method for stacked microstrip antennas taking the shape of the radiating elements, the junction of the probe, and the non-constant feed current into account. The electric characteristics of the antennas are computed rapidly View full abstract»

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  • General localised junction model in the analysis of wire-to-plate junctions

    Page(s): 1 - 7
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    A new entire-domain Galerkin method for the analysis of wire-to-plate junctions is presented. The formulation avoids additional attachment modes for modelling the junctions. Instead, a specific segmentation technique of wires and plates is proposed, based on the so-called general localised junction model. According to this model, any localised junction can be considered to consist of ends of curvilinear cylinders (wires) and adjacent sides of generalised quadrangles (plates), situated in an electrically small junction domain. The interconnections of the wire ends and plate sides can be omitted from the geometrical model, provided the current expansions for the wires and quadrangles are adopted in such a manner that the total current flowing out from the junction is zero. Numerical results obtained by the proposed method indicate that its efficiency is comparable to that based on the application of attachment modes. In addition, it enables a unified treatment of practically any junction, even those for which attachment modes have not yet been developed, whereas the classical approach requires a specific attachment mode to be defined for individual junction types View full abstract»

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  • Correction of satellite beacon propagation data using radiometer measurements

    Page(s): 62 - 64
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    Virginia Polytechnic Institute and State University has performed a comprehensive set of propagation measurements using the Olympus satellite beacons at 12.5, 20 and 30 GHz. Total-power radiometers were included in each terminal. Radiometer data were used both to set the absolute level of the beacon data and to predict path attenuation. The paper shows how radiometer data are used to correct beacon data for spacecraft-induced diurnal fluctuations and to extract clear-air attenuation View full abstract»

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  • Performance of Zolotarev and modified-Zolotarev difference pattern array distributions

    Page(s): 37 - 44
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    The Zolotarev polynomial distribution is optimum for difference pattern synthesis in the same sense as the Dolph-Chebyshev distribution is for sum synthesis. In this paper the results of a comprehensive numerical evaluation of Zolotarev arrays are used to summarise the principal features of the distribution. It is demonstrated that many of these characteristics parallel those of its sum counterpart. A tapered-sidelobe difference pattern synthesis technique is then outlined, which parallels the generalised Villeneuve n¯ distribution approach of sum patterns. Just as the Villeneuve procedure provides the array excitations for a discrete `Taylor-like' distribution directly, so the present procedure allows direct synthesis of discrete `Bayliss-like' distributions. In addition the approach is extended to incorporate a parameter which controls the sidelobe envelope taper rate View full abstract»

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  • Edge-wave diffraction for flat-plate structures

    Page(s): 30 - 36
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    An engineering approximation of the edge-guided wave contribution to radar cross-section (RCS) calculations is investigated. A dyadic diffraction coefficient is extrapolated from the representation of the edge-wave diffraction mechanisms associated with a dipole radiating in the close vicinity of the edge of a trihedron. The edge wave excited by the tip of a vertex and guided along an edge is derived from reciprocity. The rediffraction of the edge-guided fields is evaluated via multiplication with the proper edge-wave vertex diffraction coefficient. RCS calculations and time-domain extraction techniques are employed to assess and validate edge-wave diffractions from a flat plate, in comparison with method of moments computations and measured data View full abstract»

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