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Microwaves, Antennas and Propagation, IEE Proceedings H

Issue 2 • Date Apr 1992

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Displaying Results 1 - 17 of 17
  • Tensor-based characteristic impedance calculations of microstrips on ferrite-dielectric substrates for integrated phase shifter applications

    Page(s): 125 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    The influences of tensor parameters on the characteristics of microstrip structures on layered ferrite-dielectric substrates for phase shifter applications are investigated. By fully incorporating the permeability tensor into the numerical model, it is found that the propagation constant, and particularly the characteristic impedance values, are substantially lower than those commonly calculated under the scalar permeability assumption. The variation of the characteristic impedance is presented with respect to magnetisation levels, saturation magnetisations and the thickness of the ferrite layer View full abstract»

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  • Far-field computation from amplitude near-field data on two surfaces: cylindrical case

    Page(s): 143 - 148
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    A near-field far-field transformation technique involving the amplitude of the measured data has been recently proposed. It requires two sets of near-zone amplitude measurements and relies upon a mean-square fitting of the measured amplitude by an iterative projection algorithm. In the paper the method is applied to the case of cylindrical scanning, for which all the details are explicitly worked out. Furthermore the probe effect is accounted for and the relative correction procedure is considered. The relevance of a rough phase estimate and/or a general knowledge of the source is also discussed to overcome the difficulties related to the presence of local minima which can trap the procedure. Numerical examples validating the effectiveness of the technique are provided View full abstract»

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  • Improved nonlinear model for multisignal analysis of helix TWTs

    Page(s): 129 - 134
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    A simplified and improved approach for the one-dimensional nonlinear multisignal analysis of a complete helix TWT has been developed. The model takes into account both the loss and circuit variation along a tube and the inherent backward wave and reflections due to mismatch at the input and output couplers. The model is generalised to consider any number of simultaneous signals, including generation of higher-order harmonics and intermodulation components. It is fast, for interactive use, and takes less than two minutes on a Micro-Vax computer to determine the detailed characteristics of a typical tube for four-signal operation with frequencies separated by nearly 10%. The energy balance factor is satisfied within±1%, even at saturation. The accuracy of the model was checked by comparing computed results with published and experimental results for different types of helix TWT View full abstract»

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  • Superconducting microwave resonators

    Page(s): 149 - 156
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    The low surface resistance of high temperature superconductors enables the construction of resonators which have significantly higher 𝒬s than equivalent resonators made out of conventional conductors. Resonators are widely used in microwave work in many different applications, and it is therefore important to assess the performance of different types of resonant device to ascertain the improvement which is possible for each particular type. Experimental results on four different resonators are reported here, the cylindrical cavity, coaxial cavity, helical cavity and a coplanar resonator. The resonators have been constructed out of different high-temperature superconducting materials View full abstract»

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  • Slotted parallel-plate waveguide coupled to a conducting cylinder

    Page(s): 193 - 201
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    The problem of electromagnetic scattering from a perfectly electrically conducting cylinder in the presence of a slot in a parallel-plate waveguide is considered. A two-dimensional slot in one of the walls of the parallel-plate guide opens into a half-space in which the two-dimensional conducting cylinder resides. The excitation for this structure is an incident TEM wave from within the waveguide, and/or a magnetic line source which produces an incident TEy wave in the exterior half-space. Coupled integral equations for the aperture electric field and the cylinder current are derived from first principles and are solved numerically for cylinders of various cross-section, size, and location relative to that of the slot aperture. From knowledge of the aperture electric field and cylinder current, all other quantities of interest may be determined. For TEM excitation from within the guide, the reflection coefficient and radiation pattern data are presented along with the aperture electric field and cylinder current. For external excitation, data are presented that illustrate how the cylinder serves as a shield for the aperture. From this data one can assess the effectiveness of a conducting shield placed over, but not in contact with, the guide aperture View full abstract»

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  • Phase shifters for dielectric guides

    Page(s): 202 - 204
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    A phase shifter has been designed to give a constant phase over the octave bandwidth 70-140 GHz in dielectric guide. The phase shifter was designed for use in a multistate reflectometer in dielectric guide, though other applications are possible. The multistate reflectometer required two less power meters than a previous six-port reflectometer. The whole device enabled very accurate measurement of phase and amplitude in the range 70-140 GHz for little more than the cost of a swept source View full abstract»

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  • Three-pole dielectric resonator microwave bandpass active filter

    Page(s): 205 - 207
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    A lossless microwave dielectric resonator (DR) active filter is presented. Equivalent circuits for a dielectric resonator coupled to a microstrip line or to another dielectric resonator are developed from an electromagnetic analysis. With the overall electrical model of the passive and active filters described by a microwave CAD program, simulations and sensitivity analysis can be obtained. In the active filter circuit a feedback active loop (composed of a variable gain amplifier and a phase shifter) is coupled to the central DR of the passive filter to compensate for its losses. Measurements of temperature performance, power handling, third-order intermodulation product and noise level are included View full abstract»

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  • Simple antenna for circular polarisation

    Page(s): 157 - 158
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    A simple, single fed structure consisting of a pair of crossed dipoles connected to two angular branches which easily produces circular polarisation is proposed. This antenna, with a director, placed over a ground plane is analysed and a design example is realised and measured at 2 GHz View full abstract»

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  • Compound reflector antennas

    Page(s): 135 - 138
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    The results of an experimental study of two compound parabolic reflector antennas are reported. The reflectors were designed to have equal beamwidths at two separate frequency bands. The inner region of the reflector was formed as a conducting metallic surface; the outer region was a frequency-selective surface designed to be highly reflecting at the lower frequency band, and transmitting at the higher band. The performance of the compound reflector is compared with that of an equivalent wholly metallic paraboloid View full abstract»

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  • Improvements in ultra-broadband TEM coupler design

    Page(s): 171 - 178
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    A procedure which extracts the coupling factor profile from S -parameter measurements of a tapered directional coupler is presented. The difference between implemented and theoretical coupling is used together with knowledge of the cross-sectional dimensions of the coupler to produce a refined coupler design with a more ideal frequency response. Results showing the performance improvements using this technique are presented for a 3 dB quadrature coupler covering 750 MHz-26.5 GHz View full abstract»

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  • Use of subsectional edge expansion functions (SEEFs) to analyse rectangular microstrip antennas with the method of moments

    Page(s): 159 - 164
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    The technique of solving integral equations describing a microstrip antenna structure using the method of moments is well known and widely used. In the paper an efficient procedure is given to determine subsectional edge expansion functions (SEEFs) containing the correct singularities of the currents at the edges of a rectangular patch (both the current parallel and the current normal to an edge). It is proven that the use of these SEEFs considerably improves the convergence of the calculated resonant frequency. For one configuration calculated results are compared with measured values View full abstract»

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  • Study of wall region and dielectric losses in a square hard horn

    Page(s): 139 - 142
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A numerical parametric study is presented, of a circularly polarised square hard horn realised by dielectric-filled longitudinal corrugations. The horn is analysed as an open waveguide. The attenuation introduced by losses in the dielectric material is calculated from the characteristic equation of the modified TE10 mode. The far field including radiation from the walls, is found from the electric vector potential. The attenuation, aperture efficiency and crosspolar sidelobe level are presented for different dielectric linings and waveguide sizes, and are compared with the performance of the smooth-walled horn View full abstract»

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  • Electrostatic image theory of layered dielectric sphere

    Page(s): 186 - 192
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    Static image theory for a homogeneous dielectric sphere, recently formulated by one of the authors, is generalised to the problem of a multilayer dielectric sphere in terms of a line-image charge. The image line source is seen in this case to be in relation to the so-called static reflection coefficient that could be labelled as a finite Mellin transformation. This transformation is discussed and a table of corresponding transforming functions is given. The result can be applied in a more complete quasistatic analysis of interactions of layered dielectric spherical particles in an artificial dielectric media. More closely, a two-layer sphere is considered with special cases of a thin layer, and that of a low contrast between the layers. Numerical results are calculated for the radiowave propagation problem of attenuation due to melting hail particles, assumed to be composed of a spherical ice core with a spherical water shell View full abstract»

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  • Analysis of H-plane waveguide discontinuities with an improved finite-difference time domain algorithm

    Page(s): 183 - 185
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    A finite-difference time domain scheme for the analysis of H -plane waveguide discontinuities is described. The two-dimensional treatment of discontinuities and the use of a nonmonochromatic excitation allow the authors to develop an efficient algorithm with a low demand of computer resources. The method is tested by comparing the numerical results for a right corner bend and a T-junction, the choice of the absorbing boundary conditions is discussed for each case View full abstract»

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  • Extended source and load operating noise temperatures of nonlinear systems

    Page(s): 121 - 124
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    This paper proposes an extension of the source operating noise temperature and the introduction of a load operating noise temperature. These new operating noise temperatures are based on extensions of the traditional operating noise temperature and allow active as well as passive port, source and load immittances, where active and passive denote immittances with negative and positive real parts, respectively. Determination of the operating noise temperatures through the use of extended effective output noise temperatures is discussed View full abstract»

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  • Use of open-ended coaxial line sensor with a laminar or liquid dielectric backed by a conducting plane

    Page(s): 179 - 182
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    A numerical technique has been developed which enables the open-ended coaxial line sensor to be used for measurements on laminar dielectric specimens which are backed by a conducting plane. The theory, which allows the reflection coefficient of the sensor to be computed from the complex permittivity of the specimen, has been tested using an automatic network analyser for measurements on reference liquids at frequencies between 10 MHz and 3 GHz. The discrepancies between theory and measurement do not exceed the estimated measurement uncertainties, provided that the specimen is sufficiently lossy to render reflections from its perimeter negligible. The ability to measure laminar specimens is an important extension to the applications of the sensor in dielectric metrology View full abstract»

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  • Coupling processes in circular open chirowaveguides

    Page(s): 165 - 170
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The dispersion curves of circular open chirowaveguides have been obtained by two different methods. The first is based on the fulfilment of the boundary conditions at the surface of the guide. The second is based on the expansion of the electromagnetic fields in the chiral guide in terms of the modes propagating in the dielectric guide having the same geometry, permittivity ∈ and permeability μ. It is assumed that the chirality admittance is much smaller than √(∈/μ). The frequency behaviour of the dispersion curves and the coupling processes occurring between the modes along the guide are analysed View full abstract»

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