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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 5 • Date Oct 1995

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Displaying Results 1 - 11 of 11
  • Complete scattering parameter characterisation by FDTD method of Y-junction power dividers with small output angles

    Publication Year: 1995
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    The finite difference time-domain method is applied to calculate the complete frequency dependent scattering matrix of microstrip Y-junctions with increasingly narrow angles between their output ports. The results of the junctions' port isolations are presented. Numerical results obtained compare favourably with experiment and published results over a wide frequency range. These results show that the angle between the output ports significantly influences the matching, transmission and isolation characteristics of the junctions. It is shown how the stability criterion can be used to calculate a suitable size of the computational domain for accurate results. Transient spatial distribution of the electric fields of the Y-junction vividly reveals the complex mechanism of substrate surface-wave generation View full abstract»

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  • Novel slow-wave structure for narrow-band quasi-transversal filters

    Publication Year: 1995
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    Slow-wave transmission lines for producing large delays have employed multilayer patterning, increased width, or very fine features requiring accurate photolithography. A narrow-band slow-wave structure with none of these disadvantages is proposed for use with tapped delay line (transversal) narrow-band filters. This line has periodic discontinuities, resulting in a pass- and stopband structure in which the group delay in the passbands is several times that of an ordinary transmission line. The discontinuities are spaced typically by one or two wavelengths so that fine details are avoided. A linear-phase transversal stripline filter in which delay is increased by a factor of five is demonstrated. Using a previously published design procedure to calculate the filter tap weights, multiple reflections, dispersion and frequency-dependent losses were allowed for and both amplitude and phase of the filter were synthesised. A wide range of both phase and amplitude characteristics should eventually be possible and superconducting delay lines should ultimately permit losses of only 1 or 2 dB View full abstract»

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  • Variable beamwidth reflector antenna by feed defocusing

    Publication Year: 1995
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    The beamwidth of a reflector antenna may be varied by defocusing the feed. The radiation characteristics are studied for both axisymmetric and offset single reflector antennas using both geometric optics for understanding the operation and physical optics for a parametric study. The beamwidth may be increased by over 200% compared to the focused reflector before the main beam bifurcates, but the on-axis gain is reduced. Better performance is obtained with an offset reflector antenna. The study quantifies the limits of beam broadening which can be achieved. Measurements on a 30 GHz experimental antenna show good agreement with theory View full abstract»

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  • Analysis of electromagnetic scattering by artificially soft discs

    Publication Year: 1995
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    An analysis of the electromagnetic behaviour of corrugated artificially soft discs, illuminated by a vertical dipole, was carried out by using both numerical and asymptotic methods. The finite-difference time-domain method was used to find near-field distributions. This allows the consistency of the artificially soft model to be tested; furthermore, the near-field data are used to find the radiation pattern by using near-to-far-field transformations. The direct scattering in the far zone was also obtained by using edge integration of incremental diffraction coefficients; these are derived by applying the localisation process of the incremental theory of diffraction to a wedge with perfectly soft boundary conditions on one face and perfectly electric boundary conditions on the other. The effect of the corrugations is analysed in the far-field limit by comparison with a perfectly conducting disc View full abstract»

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  • Analysis of 3D microwave cavities using hierarchal vector finite elements

    Publication Year: 1995
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    A set of hierarchal vector finite elements is used to predict the resonances of 3D microwave cavities. The elements are higher-order versions of an established curvilinear brick element. Like this element, they impose only tangential continuity on the field, and are therefore suitable for modelling abrupt material interfaces and sharp corners. They are also of mixed polynomial order to avoid spurious modes. Each element in the set is formed from lower elements by adding basis functions of higher polynomial order; the set is therefore hierarchal, and different element orders can be used side by side in the same mesh. The elements are applied to a number of resonance problems with known solutions: a cube, an empty cylindrical cavity, a length of ridge waveguide, a dielectric-loaded rectangular cavity and an enclosed microstrip patch View full abstract»

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  • Eigensusceptances and eigenreactances of symmetrical waveguide inductive obstacles using the finite element method

    Publication Year: 1995
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    The eigenadmittance or eigenreactance approach has often been used to simplify the treatment of symmetrical microwave networks. The author shows that it may also be used to simplify the evaluation of symmetrical waveguide obstacles by the finite element method. An accurate value for the susceptance B of a rectangular obstacle is obtained with only 40 fourth-order elements View full abstract»

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  • Analysis of periodic fin line resonators

    Publication Year: 1995
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    The paper presents the analysis of periodic end-coupled resonators in fin line, using the space-spectral domain approach (SSDA). The flexibility of the SSDA is demonstrated for studying the periodic resonators in the fin line by incorporating the periodic boundary conditions. As an example, the resonant characteristics of the periodic end-coupled rectangular slot resonators are computed in unilateral fin line configuration View full abstract»

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  • Q-factor measurement with a scalar network analyser

    Publication Year: 1995
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    An accurate determination of the unloaded Q-factor of RF and microwave resonators is required when the electrical properties of materials are being measured or when the resonator is to be characterised for an application in a filter or an oscillator. A procedure is described of weighted least-square curve fitting to the measured magnitude of the reflection coefficient. The accuracy of the results is significantly improved by incorporating coupling losses in the equivalent circuit model View full abstract»

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  • Large-signal temperature-dependent DC model for heterojunction bipolar transistors

    Publication Year: 1995
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    A novel temperature-dependent HBT DC model in a suitable form for implementation in nonlinear circuit simulators is presented. The proposed model is accurate in all operating regions, and its parameters can be extracted easily using suitable optimisation codes. The validity and accuracy of the proposed model are confirmed by comparison to measured DC I-V characteristics of both low-power and high-power devices over a wide temperature range View full abstract»

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  • High Q-factor open resonator measurement system for 94 GHz waveband applications

    Publication Year: 1995
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    A high Q-factor hemispherical open resonator measurement system for 94 GHz waveband application is present in the paper. The analysis results on the Q-factor have been used in the design of the open resonator. Theoretical and experimental results have been obtained. The measured Q-factor of the designed open resonator is as high as 2.50×105. In this system, a PLL millimetre VCO source is employed and the measure process is controlled by a programmed computer View full abstract»

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  • Modelling and measurements of channel impulse response for an indoor wireless communication system

    Publication Year: 1995
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    The paper presents a three-dimensional vector propagation model applicable to an indoor wireless communication system, in which the scatterers are grouped into two categories, i.e. deterministic scatterers and randomly distributed scatterers. Exact information on locations and dimensions are used for the former category, while the rest of the scatterers are assumed to be randomly distributed with estimated statistical parameters. The model is based on the uniform theory of diffraction (UTD), multiple-image theory and a ray-launching technique to include all possible reflections and diffractions from ceiling, floor, walls, columns, edges and corners. Theoretical results of the power delay profiles and root-mean-square delay spreads are compared with indoor measurements done in Ottawa and Kyoto published by other authors. The good agreement with these measurements indicates that our model works well for such indoor microcellular communication applications View full abstract»

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