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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 2 • Date Apr 1998

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Displaying Results 1 - 11 of 11
  • Influence of air humidity on microwave depolarisation in semi-arid areas

    Page(s): 147 - 152
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    The subject of the work is the role of synoptic conditions in a change in the original polarisation of an electromagnetic field. The depolarisation may be provoked by any inhomogeneities in the structure of the medium. More or less dense volumes are randomly formed by the large number of solid nuclei suspended in humid air and attracting water vapour; especially in the ground atmosphere of the Northern Negev desert, where high levels of coarse aerosol concentration and humidity are typical. The electrical features of such irregularities are characterised by the permittivity of the suspended grains ε, which depends on the rate of nuclear moistening. Since ε differs strongly from the permittivity of clear air, displacement of the incoming wave from its original orientation takes place. The dependence on ε of the amount of reradiated power (received as an additional field component orthogonal to the primary transmitted signal) is assessed according to the theory of depolarisation and the Rayleigh approximation. After the removal of the meteorological factors (from six recorded parameters), the relative humidity is found to be a main parameter influencing the depolarisation rate; the rate is observed to be proportional to the humidity level View full abstract»

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  • Design of a wideband microstrip bowtie patch antenna

    Page(s): 137 - 140
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    A novel methodology is presented for the design of a wideband microstrip bowtie patch antenna of finite length placed on a dielectric substrate. The method presented is fast, computationally undemanding and reasonably accurate. This methodology is motivated by the observed array effect of the two trapezoidal halves on a single bowtie antenna. A single trapezoidal side is first designed and two such identical sides are then joined together at the apex and matched to a coaxial feed via sections of microstrip lines at the second-order resonance frequency. Experimental measurements for a bowtie designed in the X-band are shown to agree well with the simulated predictions. The bandwidth obtained was a significant 10.6% View full abstract»

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  • Performance of the progressive numerical method and its comparison with the modified spatial decomposition technique in solving large scattering problems

    Page(s): 169 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Techniques for solving electromagnetic scattering from electrically large structures are studied. Two techniques, the progressive numerical method (PNM) and the spatial decomposition technique (SDT), are applied to study the two-dimensional problems of perfectly conducting objects with TM and TE plane wave illuminations. Both PNM and SDT are based on the method of moments (MoM) and divide the objects into a number of small regions and hence reduce the matrix size and computer time. The PNM uses the concept of overlapping regions. Accurate solutions can be obtained for the TM case and good agreement with the full matrix MoM can be achieved for the TE case. It is found that the SDT needs modification, by not taking into account the virtual interface currents between the two adjacent regions and the procedure is only useful for the TM case. It is also shown that, the modified SDT is a special case of PNM in which there is no overlapping region. Finally, it is found that the PNM is an efficient way to eliminate the internal resonances of scattering problems View full abstract»

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  • Analysis of the far-field pattern of an optical waveguide array using the finite-difference beam-propagation method

    Page(s): 175 - 178
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    The far-field patterns of an optical phased array composed of three slab waveguides are investigated using the beam propagation method. The effects of mutual coupling among the waveguides on the far-field pattern are discussed for the case of zero- and five-degree deflections View full abstract»

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  • Detection of submillimetre wave radiation of a target using a high Tc superconducting detector

    Page(s): 190 - 192
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    Submillimetre wavelength (SMMW) radiation characteristics of targets are studied by undertaking experiments in which an advanced superconducting detector is used. The radiation energy in different SMMW bands can be researched and analysed theoretically and experimentally by means of a group of formulas and filters View full abstract»

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  • Simple approach to determine resonant frequencies of microstrip antennas

    Page(s): 159 - 162
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A simple approach for accurate determination of the resonant frequencies of microstrip antennas of regular geometries is developed and presented. In this approach, a generalised empirical formula for the computation of effective dielectric permittivity is given which takes into account the ratio of the fringing area to the area of the patch. A correction to the equivalent side length of an equilateral triangular patch, previously published, is modified and a new formula is given. A correction to the effective dimensions of an elliptical microstrip antenna is also carried out. Numerical results obtained for the resonant frequencies of elliptical, circular, rectangular and equilateral-triangular microstrip antennas are in good agreement with the available theoretical and experimental results reported by others. The present approach is more efficient, simpler and more accurate View full abstract»

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  • Numerical optimisation of slot parameters for a concentric array radial line slot antenna

    Page(s): 141 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    Numerical slot design of a concentric array radial line slot antenna (CA-RLSA) with matching slots is proposed for small aperture antennas. In contrast to the previous design for large aperture RLSAs based upon continuous source model, the parameters of discrete slots in the finite aperture are directly determined for uniform excitation. A remarkable efficiency of 85%, and 82%, is measured for 24 cm and 16 cm diameter antennas, respectively View full abstract»

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  • Reflection and transmission coefficients for thin bianisotropic layers

    Page(s): 163 - 168
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    The paper present approximate analytical solutions for reflection and transmission coefficients of general uniaxial bianisotropic media slabs. The analysis is based on generalised second-order impedance boundary conditions (GIBC) simulating bianisotropic slabs. The GIBC are obtained using the averaging procedure. Layers much thinner than the wavelength are considered. The results are tested by comparing the approximate reflection coefficients from an uniaxial bianisotropic layer with the exact solution View full abstract»

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  • Combined EM field/linear and nonlinear circuit simulation using the FDTD method

    Page(s): 185 - 189
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    A review of several techniques related to the combination of geometrical decomposition of mixed geometry problems coupled with the inclusion of single and multiple linear and nonlinear circuit elements is addressed for use with the FDTD method. As a demonstrator of the algorithmic aspects related to this problem, a slot loop antenna is analysed. Several variants of the antenna are described, the simplest variation consisting of a slot loop antenna fed by a coplanar waveguide line connected via a slotline transition. More elaborate variations include techniques for the inclusion of lumped linear and/or nonlinear elements into the FDTD code. The inclusion of three terminal lumped active devices is demonstrated in order to describe the algorithmic details of the slot loop operated as an active antenna. Where possible, experimental and theoretical predictions are compared in order to validate the methodologies adopted View full abstract»

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  • Features of creeping waves propagation on the dielectric-coated circular cylinder

    Page(s): 179 - 184
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    For the first time, the 2-D circular PEC cylinder coated with a uniform layer of lossy dielectric is numerically investigated. The complex propagation constants of the first three creeping wave modes are calculated for the case of a coating thickness increase from 0 to d/λ0=0.5. The dependence of the constants on the dielectric losses is studied and the `critical losses' effect is observed for the higher order modes. It consists of leaky modes transition to trapped modes for a definite value of dielectric constant ε View full abstract»

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  • Beamforming for circular and semicircular array antennas for low-cost wireless LAN data communications systems

    Page(s): 153 - 158
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    An investigation into beam synthesis for small circular and semicircular arrays is presented. Array antennas of this type are likely to become a core component in future wireless LAN systems architecture. They offer additional spatial diversity as a means for combating multipath interference, necessary for high speed data communications, and user mobility. Beams are synthesised using cophasal and adaptive algorithms. Beamwidths of 19° and -20 dB sidelobe levels are attainable from an array of three wavelengths diameter. A semicircular array of this type can maintain a gain of approximately 10 dBi over a look direction angular range of ±50° View full abstract»

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