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1887

IEE Proceedings H (Microwaves, Antennas and Propagation)

Volume 134, Issue 1, February 1987

Volumes & issues:

Volume 134, Issue 1

February 1987

Effects of an intervening airgap on the two fundamental modes of a surface waveguide
Erratum: Simple models for high-frequency MESFETS and comparison with experimental results
Variational method for coplanar waveguide with anisotropic substrates
New method for the analysis of dual-gate MESFET mixers
  • Author(s): J. Dreifuss ; A. Madjar ; A. Bar-lev
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 11 –15
  • DOI:  10.1049/ip-h-2.1987.0004
  • Type: Article
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  • p. 11 –15 (5)
    A method for the analysis of a microwave mixer based on a dual-gate MESFET is presented. The method extends a previously published analysis technique for a single-gate MESFET mixer by treating the circuit as a threeport network. The device is described by a complete mathematical model and the harmonic balance technique is utilised for the large-signal analysis stage. This results in a relatively fast program. The method is demonstrated by applying it to the simulation of a mixer based on a Raytheon transistor RDX832 for which device data was available. The mixer was constructed and its experimentally obtained performance results show good agreement between the simulated and the measured conversion gain values through a wide range of local-oscillator input power.
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Rigorous analysis of dielectric rod waveguides with flat cross-section
  • Author(s): T. Miyamoto
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 16 –24
  • DOI:  10.1049/ip-h-2.1987.0005
  • Type: Article
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  • p. 16 –24 (9)
    The mode-matching method is applied to the rigorous investigation of propagation characteristics of rod waveguides, such as an elliptically cored optical fibre or a rectangular waveguide with a flat cross-section, whose accurate analysis has been difficult so far. A high accuracy, to five significant figures, is achieved for the normalised propagation constant. Field distributions in several hybrid modes, as well as dispersion relations, are detailed. It is also confirmed that the hybrid mode analysis is not always necessary in the case of flat cross-section. The properties of higher-order mode cutoff and polarisation preservation in an elliptically cored fibre, whose investigation has not been always sufficient, are discussed more accurately. Through these analyses, it is also confirmed that the mode matching method is still a useful and reliable numerical method for rigorous analysis of the rodtype dielectric waveguide with an arbitrarily shaped cross-section
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Implementation of microwave diffraction tomography for measurement of dielectric constant distribution
  • Author(s): F.J. Paoloni
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 25 –29
  • DOI:  10.1049/ip-h-2.1987.0006
  • Type: Article
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  • p. 25 –29 (5)
    Diffraction tomography is a process that can infer the internal structure of an object from multiple views of its diffraction shadow. The procedure is sensitive to variations in the object's refractive index and there is interest in using the technique to measure permittivity distributions within dielectric objects and to image soft tissues for biomedical applications. To allow the inversion to proceed, a number of conditions have to be met. These determine the type of object to be studied, the geometry of the microwave system and surrounding environment. The optimal resolution distance obtainable is half a wavelength, but this can rarely be achieved because of practical limitations. Some procedures, however, are available to improve the practical resolution. One, which is suitable for microwave tomography, is to use multifrequency data and to combine the resulting images. A system operating over the X-Band microwave frequency range is described and some results for test objects in air are given
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Wavefront quality in antenna pattern measurement: the use of residuals
  • Author(s): J.C. Bennett  and  K.S. Farhat
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 30 –34
  • DOI:  10.1049/ip-h-2.1987.0007
  • Type: Article
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  • p. 30 –34 (5)
    The concept of the far-field residual source distribution is presented as a convenient and accurate means of assessing the quality of a wavefront employed in antenna measurements. The residual defines the errors in radiation pattern measurements in terms of the plane wavefront quality of the technique employed and can be used to examine the far-field range, the compact range and the near-field/far-field transformation. It is shown that the spherical wavefront of the farfield range can be analytically decomposed into a residual spectrum which can be used to explain the classical errors found in radiation patterns measured at a finite distance. The significance of different types of illumination is examined for the compact range. It is demonstrated that heavily tapered distributions can provide high accuracy at wide angles, whereas more uniform illumination results in better accuracy for near-in sidelobe measurements. Finally, the residual is used to quantify the accuracy offered by the near-field/far-field transformation and, as expected, demonstrates this to be the most accurate antenna measurement technique available
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Novel cylindrical-wave spectrum for analysis of scattering by multiple bodies
  • Author(s): A.Z. Elsherbeni  and  M. Hamid
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 35 –44
  • DOI:  10.1049/ip-h-2.1987.0008
  • Type: Article
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  • p. 35 –44 (10)
    A new technique based on the spectrum of cylindrical waves and successive scattering is developed to evaluate the scattered field due to two parallel cylindrical scatterers to any desired degree of accuracy. The salient features of the method are discussed and the results are presented for some practical configurations, namely two parallel circular cylinders and two semi-infinite wedges. The proposed technique is also applicable for scattering by multiple bodies of arbitrary cross-sectional shape once the scattering by each body in isolation is manageable. The numerical results for the scattering by two cylinders agree with the available exact boundary-value solution, whereas for the double wedge the transmission coefficient compares favourably with the exact values for the special case of a slit geometry and with two other asymptotic solutions for wide separations
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Noise considerations in active monopoles
Simplified design procedures for Butler matrices incorporating 90° hybrids or 180° hybrids
Role of particle-size distributions on millimetre-wave propagation in sand/dust storms
  • Author(s): A.S. Ahmed
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 55 –59
  • DOI:  10.1049/ip-h-2.1987.0011
  • Type: Article
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  • p. 55 –59 (5)
    Particle size distributions of sand and dust are surveyed. Various assumptions for the theoretical prediction of the effect of particles on MMW propagation are discussed and justified. A general formula of the propagation parameters, for any particle shape and any distribution, is developed. It is found that the MMW propagation depends strongly on the probability density function of particle size distribution. A simplelinear relationship is shown between ‘α, π’ and an ‘effective radius’ of the storm. Attenuation and phase shift due to spherical and ellipsoidal particles are calculated for four distributions, namely power law, exponential, lognormal and normal. Results are presented and the role of the distributions is discussed
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Gain enhancement of antennas over finite ground plane covered by a dielectric sheet
  • Author(s): A.A. Kishk  and  L. Shafai
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 60 –64
  • DOI:  10.1049/ip-h-2.1987.0012
  • Type: Article
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  • p. 60 –64 (5)
    In the paper the problem of gain enhancement for radiating elements between two finite plane reflectors, one of which is a partial reflector and the other a perfect conductor, is investigated. The problem is studied numerically using the method of moments and the effect of different parameters is investigated. It is shown that, as is similar to infinite structures, the antenna gain can be increased with finite size reflectors. Furthermore, for finite structures, the gain enhancement can be made larger than that of infinite structures. However, for optimum gain enhancement, the structure parameters must be selected with care
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Long-range propagation experiment to investigate the incidence of anomalous propagation in the North Atlantic
  • Author(s): J. Clarke  and  G. Rider
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 65 –70
  • DOI:  10.1049/ip-h-2.1987.0013
  • Type: Article
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  • p. 65 –70 (6)
    The significance of enhanced range on air-to-ground paths is reviewed and an experiment described which collected maximum range data on an oversea path. A secondary surveillance radar sited in the Hebrides was used to observe civil air traffic crossing the North Atlantic, and a cumulative distribution of range extending to 0.1% of the year obtained based on 14 months of observation. About 99% of the observations are shown to be satisfactorily modelled by employing an exponential atmosphere with linear N profiles as measured by a suitably sited radio-sonde station to model the first 1 km of height. The remaining 1% of observations, the extreme range cases, are examined in some detail and are attributed to ray bending in passage through elevated layers
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Analysis of multipath fading on line-of-sight links in the presence of an elevated atmospheric duct
  • Author(s): S.F. Mahmoud ; H.N. Boghdady ; O.L. El-sayed
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 71 –76
  • DOI:  10.1049/ip-h-2.1987.0014
  • Type: Article
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  • p. 71 –76 (6)
    Multipath propagation on microwave line-of-sight links is analysed in the presence of an elevated inversion atmospheric layer and a reflecting earth. A bilinear height profile for the modified refractive index is adopted. Simple mathematical relations are derived for the number of rays hitting the receiver, and a graphical solution is presented for the launching and arrival angles. It is shown that path inclination tends to reduce the number of rays reaching the receiver. When more than three rays are received, signal enhancement, due to ducting, is more likely to occur. On the other hand, signal fading is more probable in the presence of two or three rays
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Angle estimation with adaptive arrays and its relation to super-resolution
Engineering model for arbitrarily shaped microstrip antennas based on the collocation method
Convergence phenomenon in the solution of dichroic scattering problems by Galerkin's method
  • Author(s): F.S. Johansson
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 87 –92
  • DOI:  10.1049/ip-h-2.1987.0017
  • Type: Article
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  • p. 87 –92 (6)
    The convergence problem that arises when the scattering problem of dichroic surfaces is solved numerically by means of Galerkin's method and Floquet's theorem is investigated. A theoretical discussion is outlined showing that a truncation of the infinite Floquet spectrum is actually equivalent to modifying the used basis functions. Examples of modified basis functions due to different Floquet-mode truncations and the effect on the numerical results are demonstrated for the particular cases of arrays of thin dipoles and crossed dipoles. Some useful truncation rules are also presented, and the theories are verified by comparing predicted values with experimental results obtained by waveguide simulator measurements
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Evaluation of Sommerfeld integrals arising in the ground stake antenna problem
  • Author(s): K.A. Michalski  and  C.M. Butler
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 134, Issue 1, p. 93 –97
  • DOI:  10.1049/ip-h-2.1987.0018
  • Type: Article
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  • p. 93 –97 (5)
    A novel approach is described to the numerical evaluation of Sommerfeld integrals, which offers a compromise between efficiency and simplicity. In this method, the real-axis path of integration is deformed to a contour, which is the steepest-descent path for the exponential function present in the integrand. This new contour also avoids the singularities of the integrand which occur near the original path. The proposed technique is applicable if the radial displacement of the source and field points is electrically small and is most efficient if this displacement is smaller than the vertical separation between these points. Such conditions prevail, for example, in the analysis by means of the integral equation technique of a thin, vertical wire antenna, which penetrates the interface between two media (the so-called ground stake antenna)
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Technical memorandum: Conductance Of A Longitudinal, Resonant Slot In A Ridge Waveguide
Single Sided Slotline Microstrip Transition
New method for the measurement of coupling coefficients of transmission cavities
Technical memorandum: Highly Shaped Beam Telemetry Antenna For The ERS-1 Satellite

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