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IEE Proceedings H (Microwaves, Antennas and Propagation)

Volume 140, Issue 4, August 1993

Volumes & issues:

Volume 140, Issue 4

August 1993

Electromagnetic scattering from arbitrarily shaped conducting bodies coated with a thin layer off lossy magnetic material
  • Author(s): A. Sadigh  and  E. Arvas
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 249 –253
  • DOI:  10.1049/ip-h-2.1993.0036
  • Type: Article
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  • p. 249 –253 (5)
    An efficient moment solution is given for the problem of electromagnetic scattering from an arbitrarily shaped, three-dimensional conducting body coated with a thin layer of lossy magnetic material. The surface equivalence principle is used to replace the conductor with a surface electric current, and the volume equivalence principle is used to replace the coating with a magnetic volume current. The behaviour of the field in the thin coating justifies approximating the volume current by a surface magnetic current residing next to the surface electric current. The boundary condition on the tangential component of the total magnetic field is used to express the magnetic surface current in terms of the electric surface current. The boundary condition on the tangential component of the electric field is then used to obtain an integral equation for the surface current. The method of moments is used to solve this equation approximately. The computed numerical results are in excellent agreement with the exact data for the case of a spherical scatterer.
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Propagation characteristics of circular chirowaveguides periodically loaded with metal gratings
Frequency-domain-continuation intermodulation-balance method for the analysis of nonlinear microwave circuits with multifrequency excitations
  • Author(s): X. Zeng
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 259 –262
  • DOI:  10.1049/ip-h-2.1993.0038
  • Type: Article
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  • p. 259 –262 (4)
    The paper proposes an analysis method of nonlinear microwave circuits referred to as the frequency-domain-continuation intermodulation balance method (FDCIBM). This technique introduces a generalised complex matrix to represent (in the frequency domain) the steady-state variables of the nonlinear circuit with multifrequency large-signal excitation. In terms of this generalised complex matrix and a generalised complex-matrix convolution operator defined here, the frequencydomain- balance equation of the nonlinear circuit is a system of complex-variable nonlinear algebraic equations, that is solved using the continuation method. As an example, the intermodulation analysis of a GaAs MESFET amplifier is given.
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Hybrid antenna synthesis for reconfigurable contoured beams
  • Author(s): A.D. Searle  and  B.S. Westcott
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 263 –268
  • DOI:  10.1049/ip-h-2.1993.0039
  • Type: Article
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  • p. 263 –268 (6)
    A reflector illuminated by a small phased array is an attractive antenna configuration for systems requiring reconfigurable contoured beams. The use of a shaped reflector can provide control of the feed power distribution and antenna geometry. A systematic reflector synthesis technique based on geometric optics is formulated, using complex coordinate notation and illustrated by application to a simple design requirement. Results demonstrate that geometric shaping can be successfully applied to systems with distributed sources, and that significant beam reconfiguration can be achieved by phase-only control of the feed array.
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Analysis of quadrifilar resonant printed helical antenna for mobile communications
Synthesis of eight-port comparator circuits using Dicke's methods
Alternative derivation of the cascaded cylinder diffraction model
  • Author(s): D.E. Eliades
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 279 –284
  • DOI:  10.1049/ip-h-2.1993.0042
  • Type: Article
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  • p. 279 –284 (6)
    By making use of rigorous solution to the problem of electromagnetic wave propagation as given by the compensation theorem, a qualitative justification for the existence of a number of models in which the prominent terrain features are replaced by simple geometrical shapes and for which canonical solutions exist is presented. The paper presents an alternative derivation of the recently introduced cascaded cylinder model, which considers propagation by diffraction over a cascaded arrangement of circular cylinders. The model predictions are compared with experimental data, and with Vogler's multiple halfplane function.
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Terrain simulation for the cascaded cylinder diffraction model
  • Author(s): D.E. Eliades
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 285 –291
  • DOI:  10.1049/ip-h-2.1993.0043
  • Type: Article
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  • p. 285 –291 (7)
    An algorithm is presented which makes use of a topographical and a morphological terrain database to simulate the terrain profile along the great cricle path between a transmitter and a receiver by a cascaded arrangement of circular cylinders. This idealised representation is used by the recently introduced cascaded cylinder diffraction model to predict the propagation loss along the geodesic path. Prior to making use of the terrain data, it is corrected for the earth's curvature and for the atmospheric radio refractive index. An approximate but efficient interpolation scheme, using bi-cubic B-splines is employed to compute terrain surface heights and their first and second-order derivatives. Using these tools, a technique for detecting the prominent terrain obstacles along the geodesic profile is presented. Finally, each identified terrain feature is simulated by an optimum cylinder fit. Verification of the model is presented by comparing its predictions with experimental results.
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Wideband filters employing multilayer gratings
  • Author(s): P.W.B. Au ; E.A. Parker ; R.J. Langley
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 292 –296
  • DOI:  10.1049/ip-h-2.1993.0044
  • Type: Article
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  • p. 292 –296 (5)
    Multilayer surfaces, consisting of stacked inductive and capacitive strips or grids, have been used to design wideband filters in the 5–40 GHz range, with rapid transitions between reflection and transmission. For singly polarised applications, transmission bandwidths of 70–100% and edge transition ratios of 1.1–1.3 are realisable at 45° TM incidence using 4–8 layers of capacitive and inductive strips. Factors which constrain the passbands are highlighted. In dual polarised designs using doubly periodic grids, the widths are restricted to 35–40% by TE incidence grating responses at the upper passband edge. In TM they are even more restricted by a TE11 mode resonance. Wider passbands require high inductances to reduce the low frequency edge, implying very fine conductors.
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Statistics of short time and spatial variations measured in wideband indoor radio channels
  • Author(s): R. Ganesh  and  K. Pahlavan
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 297 –302
  • DOI:  10.1049/ip-h-2.1993.0045
  • Type: Article
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  • p. 297 –302 (6)
    In an indoor environment, channel variations which occur most frequently are due to the movement of personnel near the transmitting or receiving antennas and/or local movements of the terminals around a given location. Such spatial and short time variations in the indoor radio channel are studied and determined by performing wideband propagation experiments in line of sight and nonline of sight environments at 910 MHz. The database is divided into two classes: spatial and short time variations. Spatial variations deal with the changes in the radio channel, observed over a short time and space, at different locations in an environment. The short time variations address changes induced over time, by human traffic close to the fixed transmitter/receiver or by manually shaking the antenna on its base. The statistics of RMS delay spread and the received power in the multipath profiles are computed and compared for these experimental variations.
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Stacked resonators for bandwidth enhancement: a comparison of two feeding techniques
Shielding of single- and double-reflector earth station antennas: a near- and far-field approach
  • Author(s): G.A.J. van Dooren  and  H.J.F.G. Govaerts
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 309 –314
  • DOI:  10.1049/ip-h-2.1993.0047
  • Type: Article
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  • p. 309 –314 (6)
    The paper describes the off-axis radiation pattern calculation of a Cassegrain antenna system with prescribed geometrical parameters, in the absence and presence of a (hypothetical) halfplane obstacle located either in the near or far field of the antenna. The attenuation caused by the obstacle as a function of antenna orientation and position is calculated and presented. The results for the halfplane shielding of the double-reflector system are compared with those obtained for a single-reflector antenna system shielded by the same obstacle. Three different, but related, approaches for calculating the additional propagation loss are presented and compared. It is found that the proposed near-field approach gives the best overall results.
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Neural network approach to prediction of terrestrial wave propagation for mobile radio
  • Author(s): K.E. Stocker ; B.E. Gschwendtner ; F.M. Landstorfer
  • Source: IEE Proceedings H (Microwaves, Antennas and Propagation), Volume 140, Issue 4, p. 315 –320
  • DOI:  10.1049/ip-h-2.1993.0048
  • Type: Article
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  • p. 315 –320 (6)
    Theoretical investigations into the suitability of neural network simulators for the prediction of field strength based on topographical and morphographical data are presented. Effective input and output data processing is developed using deterministic and heuristic formulae for the training of a neural network simulator. First successful steps towards a planning tool for mobile radio communication based on adaptive learning from measurement data are made. Field strength prediction with the new system shows acceptable conformity with measurements.
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CAD oriented method for noise analysis of microwave circuits described by the nodal admittance matrix
Temperature control of radar cross-section using electrically small high Tc superconducting antenna elements for stealth applications

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