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Microwaves, Antennas and Propagation, IEE Proceedings H

Issue 6 • Date Dec 1990

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Displaying Results 1 - 17 of 17
  • Simple and broadband orthomode transducer (antenna feed)

    Page(s): 396 - 400
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    A simple and broadband orthomode transducer (OMT) is presented. It can be machined or moulded in two almost identical parts which implies a potentially cheap design. Both the mechanical construction and the principle of operation are described. The paper also presents results both from some pre-experimentations and for the complete OMT. These results show that the isolation between the ports for the complete OMT is better than approximately 50 dB and the return loss less than -20 dB in the frequency range 10.0-15.0 GHz. View full abstract»

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  • Radiation from elliptical hybrid-mode waveguides

    Page(s): 417 - 420
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    The condition for circularly polarised radiation fields from waveguide apertures is discussed. It is shown that ideal circular polarisation cannot be achieved in practice for elliptical hybrid-mode waveguides, neither for corrugated nor for partly filled dielectric (dielcore) waveguides. The crosspolar performance of the elliptical dielcore waveguide supporting the fundamental hybrid-mode is calculated accurately, confirming its good crosspolar performance which has been previously shown by experiments. View full abstract»

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  • Scattering characteristics of a centre-inclined slot in a broad wall of a rectangular waveguide

    Page(s): 343 - 348
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    The problem of a centred-inclined radiating slot cut in a broad wall of a rectangular waveguide and excited by a TE10 mode wave is considered. Pertinent integral equations for the slot aperture electric field are solved using the method of moments. Scattering characteristics of the slot are then analysed including resonant length and the equivalent series impedance. Numerical results on resonant length and the normalised series impedance in a universal form are obtained over a range of values of tilt, slot width, waveguide height, wall thickness and frequency. These results should find applications in the design of arrays of centred-inclined slots. View full abstract»

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  • Moment method analysis of a slot coupled junction between dissimilar rectangular waveguides

    Page(s): 406 - 410
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    This paper presents a moment method analysis of a rectangular slot coupled transition between two dissimilar rectangular waveguides. The effect of the finite thickness of the metallic wall, in which the slot is milled, is taken into account by considering the coupling slot as a small section of a rectangular waveguide. The reflection coefficient and VSWR are evaluated for a transition between WR-90 and WR-112 rectangular waveguides. A comparison between the theoretical and experimental results on the variations of the magnitude and phase of the reflection coefficient is presented for the limiting case when the two waveguides are identical. View full abstract»

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  • Modelling of particle distribution in the melting layer

    Page(s): 389 - 395
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    The analysis of radiowave propagation through, and radar scattering from, the melting layer requires a model of the melting ice particles with appropriate statistics of shape, size, and orientation distributions. Previous studies have indicated that the melting layer can be modelled by a collection of wet snow spheroids in air, of which the effective permittivity and the volume fraction are the most important parameters. It is proposed that the distribution of spheroid shapes can be modelled by a flat probability density of depolarisation parameter lambda 3 between a minimum and a maximum value. The location of the average lambda 3 is crucial; the width is less important. View full abstract»

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  • A Coulomb gauge analysis of a wire scatterer

    Page(s): 384 - 388
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    The Lorentz gauge is the preferred gauge when problems in electromagnetic scattering and diffraction are solved by a classical Maxwell equation potential function approach. The free space magnetic vector and scalar potentials subject to the Coulomb gauge are obtained in the paper. It is shown that the Coulomb gauge vector potential dyadic Green's function can be extracted from the well known Lorentz gauge free space vector potential Green's function. The electric field mixed potential integral equation (MPIE) for a straight, circular, finite-length, narrow conducting cylinder scatterer is formulated and solved in both the Lorentz and Coulomb gauges and results are presented in terms of the cylinder surface current. The merits and drawbacks of the Coulomb gauge formulation are discussed. View full abstract»

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  • Prediction of depolarisation distributions on Earth-space paths

    Page(s): 325 - 330
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    By using the theoretical relationship between attenuation and depolarisation, a cumulative distribution of depolarisation can be predicted from a distribution of attenuation at the same frequency. In the case of Earth-space paths, however, it was found that there is poor correlation between measured attenuation and XPD because of so-called ice depolarisation. This implies that the predicted XPD value for an Earth-space path includes an error if the theoretical relationship between rain attenuation and XPD is used. In this paper, a new method of predicting cumulative distributions of XPD is proposed in which the effects of the ice depolarisation are taken into consideration by using the factor of 'ice depolarisation ratio'. The applicability of this depolarisation prediction method is verified by using attenuation and depolarisation statistics which have been measured in some wave propagation experiments along Earth-space paths. View full abstract»

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  • Admittance characteristics and far-field patterns for coupled spheroidal dipole antennas in arbitrary configuration

    Page(s): 337 - 342
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The admittance characteristics of a system consisting of two centre-fed antennas of arbitrary orientation are investigated. Each antenna is modelled by a very thin prolate spheroid which is centrally fed by a gap voltage. By using the equivalence principle, each spheroidal dipole is replaced by a solid spheroidal conductor of the same size without a gap, encircled by a corresponding filamentary ring carrying magnetic current of proper magnitude. The associated electric and magnetic fields are expanded in terms of appropriate vector spheroidal eigenfunctions and the boundary conditions at the surface of each spheroid are imposed by using the rotational-translational addition theorems for vector spheroidal wave functions. The solution of the resulting set of algebraic equations gives the unknown scattered field expansion coefficients. Numerical results are presented for the mutual admittance of two centre-fed thin spheroidal dipole antennas of arbitrary orientation, for various centre displacements. In addition, the E and H-plane patterns are computed for the system of two dipole antennas in various configurations, with one dipole being parasitic. View full abstract»

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  • Input impedance of concentric ring microstrip antennas for dual frequency band operation including surface wave coupling

    Page(s): 331 - 336
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The impedance properties of a dual concentric annular ring microstrip patch antenna are described. This patch operates at two frequency bands which may be closely spaced. The TM12 mode is primarily investigated but other modes are also treated. An equivalent circuit model for the input impedance is presented together with experimental verification. Surface waves are found to be important even for very thin substrates and these are included in the model. Factors which influence the ring design are discussed. View full abstract»

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  • Matching slot pair for a circularly-polarised slotted waveguide array

    Page(s): 367 - 371
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    A matching slot pair which radiates all the incident power in a circularly-polarised wave is proposed and analysed for use as a terminal in a leaky-wave slotted waveguide array. The position and size of the slots are numerically optimised to suppress reflection and to realise a desired polarisation in the tilted beam direction, which contributes to improving the antenna efficiency. It is verified experimentally that the return loss is below -15 dB over 0.1 GHz at the 4 GHz band and the 3 dB axial ratio bandwidth is about 5% in the tilted beam direction. View full abstract»

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  • Multiport network model for rectangular microstrip patches covered with a dielectric layer

    Page(s): 377 - 383
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    An extension of the multiport network modelling technique applied to rectangular microstrip patches on thin substrates covered with a dielectric layer is reported. The edge admittance networks for the radiating edges and the mutual coupling network for the external interaction between the two radiating edges are obtained from the spectral domain solution for fields of a magnetic current element placed on a conducting ground and covered with a dielectric layer. Results of the analysis for single-port and two-port patches are compared with experimental results. The good agreement validates the model and the analysis procedure proposed. View full abstract»

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  • Measurement error for six port ANA

    Page(s): 415 - 416
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (108 KB)  

    Although six-port ANA theory requires that the input impedances of power detectors remain constant with incident power, this is not generally the case if diode detectors are used. Consequently, uncertainties in the measurement of the unknown load reflection coefficient appear. Measurements of the variations of diode impedances are used in a computer simulation to estimate these uncertainties. View full abstract»

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  • Intersection approach to array pattern synthesis

    Page(s): 349 - 357
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    A new synthesis method based on the intersection approach is presented: the synthesis is viewed as the problem of finding the intersection of sets. This is a more natural, flexible and effective formulation of the problem but despite this it has not previously received much attention. The search for a point belonging to the intersection of two sets allows a very effective solution procedure, based on the projector concept and on a suitable choice of the starting point of the iteration. A number of one and two dimensional examples are presented to highlight the various aspects of the method. Emphasis is put on constrained array synthesis which is important when the practical realisation of the synthesised array is of concern. The method permits the synthesis of constrained patterns without appreciable degradation of the pattern desired. View full abstract»

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  • Broadside-coupled rectangular resonators in suspended stripline with single and double dielectrics

    Page(s): 411 - 414
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    The rigorous spectral domain method is applied to analyse the resonant frequency characteristics of rectangular resonators in three broadside-coupled suspended stripline configurations. These are (a) broadside-coupled suspended stripline with a single dielectric (b) broadside-coupled suspended stripline with double dielectrics and (c) broadside-coupled suspended stripline with double inverted dielectrics. Computed dominant even- and odd-mode resonant frequencies of rectangular resonators in the above broadside-coupled configurations are presented as a function of various structural parameters. These characteristics are distinct from those obtained for conventional edge-coupled microstrip resonators. The computed resonant frequencies using simple basis functions are compared with the experimental values in the frequency range 5-13 GHz. The results presented in this paper should find application in the design of microwave and millimeter wave integrated circuit components. View full abstract»

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  • Finite difference analysis of infinite arrays of two-dimensional microstrip structures

    Page(s): 358 - 366
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    Infinite arrays of two-dimensional printed elements are analysed using the finite difference method. Grid models accounting for dielectric discontinuities and current continuity at rectangular junctions are developed. The procedure is used to study the behaviour of three configurations of planar strips over dielectric substrates in an infinite array environment. These configurations include the 'dipole' element, the 'microstrip' element and the 'microstrip' element over an inhomogeneous substrate. For each configuration, calculated results are presented with special attention given to the correctness of antenna characteristics such as input impedance and scan performance. The results accurately predict antenna performance and comparison with published data confirms the method. View full abstract»

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  • Computation of Q-factors of dielectric-loaded cylindrical cavity resonators

    Page(s): 372 - 376
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    Based on the one-dimensional finite element method a general formulation is presented for the calculation of the conductor Q-factor, Qc, associated with metallic losses of cylindrical cavity resonators loaded axisymmetrically with dielectrics. The formulation is employed to accurately determine Qc relating to the first few modes of the cylindrical cavity resonator loaded with a hollow cylindrical dielectric as well as to obtain Qc relating to the fundamental mode (TE01 delta ) of the ring resonator on a microstrip substrate. View full abstract»

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  • Electromagnetic transmission through a small radome of arbitrary shape

    Page(s): 401 - 405
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    A simple moment solution is presented for the problem of electromagnetic transmission through a small radome of arbitrary shape. The radome is excited by either a plane wave (receive mode) or an elementary dipole inside the radome (transmit mode). The equivalence principle is used to replace the radome by a set of equivalent electric and magnetic surface currents radiating into an unbounded medium. A set of coupled integral equations involving the surface currents is obtained by enforcing the boundary conditions on the tangential components of the total electric and magnetic fields. The method of moments is used to solve the integral equations. The surfaces of the radome are approximated by planar triangular patches and linearly varying vector functions are used for both expansion and testing functions. In the receive mode, the total field inside the radome is computed along a number of straight lines and in the transmit mode the far transmitted field is computed. A spherical and a Von Karman radome are studied. The computed results are in excellent agreement with the exact or other available published data. View full abstract»

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