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Microwaves, Antennas and Propagation, IEE Proceedings

Issue 4 • Date Aug 1997

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Displaying Results 1 - 11 of 11
  • Design of loop antennas and matching networks for low-noise RF receivers: analytic formula approach

    Publication Year: 1997 , Page(s): 274 - 280
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A comprehensive procedure for designing loop antennas and matching networks for low-noise receivers, by using an analytical formula approach, is presented. The effective length leffect of an equivalent transmission line, for a single-turn loop antenna, and the effective coupling coefficient ρ, for a multiturn loop antenna, are introduced in the approximate formulas for the impedances of single loop as well as multiturn loop antennas, which are valid up to the first resonant frequency. Hence, an accurate design of loop antennas and matching networks of receiving systems can be achieved by using circuit analysis. The theoretical results are compared with the measured results View full abstract»

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  • Observations of Doppler spreading on HF signals propagating over high latitude paths

    Publication Year: 1997 , Page(s): 215 - 220
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    The high latitude ionosphere forms a highly dynamic and disturbed medium which can severely degrade the performance of HF radio systems when the signals propagate through these regions. One important parameter is the Doppler frequency spreading imposed on the signal by the movement of electron density irregularities in the ionosphere at the reflection points. The magnitude of the Doppler spreading has been quantified in a series of experiments undertaken on a range of frequencies across the HF band over several high latitude paths. Two of these paths are considered in this paper, one of which (Clyde River-Alert, 1345 km) was contained entirely within the polar cap whilst the second (Clyde River-Prudhoe Bay, 2955 km) was sometimes entirely within the polar cap and at other times crossed the auroral oval. Results obtained over two one-month periods, one in summer (July/August 1988) and one in winter (January/February 1989), are presented View full abstract»

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  • Moment method analysis of printed single-arm wire spiral antennas using curved segments

    Publication Year: 1997 , Page(s): 261 - 265
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    Single-arm wire spirals printed on grounded dielectric substrates are analysed using a moment method algorithm which uses piecewise sinusoidal subdomain basis and test functions on curved segments, which follow exactly the spiral curvature. Results are compared with those obtained from measurements and with published results using linear segmentation, and it is shown that the curved segment model is accurate and significantly more computationally efficient View full abstract»

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  • Results from clear-air propagation studies on Franco-UK paths at 1.3 and 11 GHz

    Publication Year: 1997 , Page(s): 267 - 273
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    The paper presents results from statistical studies of radio propagation at frequencies between 1.3 GHz and 11.7 GHz on radio paths of 153-297 km, with data collected over 8 years. Data from the first 3 years were used in COST Project 210 and related to annual average conditions. More recent data, included in the paper, have been used to study worst month statistics, signal attenuation in propagation over coastal zones and 1.3/11.7 GHz frequency scaling View full abstract»

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  • Large HF bearing errors for propagation paths contained within the polar cap

    Publication Year: 1997 , Page(s): 241 - 249
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1040 KB)  

    Large electron-density gradients in the polar-cap ionosphere, associated with the convection of patches of overdense plasma and the presence of high-latitude auroral arcs, produce tilted reflecting surfaces which result in HF signals propagating over paths well displaced from the great circle. Measurements have been made at a very high-latitude receiving site of signals propagated over paths contained within the polar cap. Systematic swings in the bearing of the received signal of up to ±100° from the great circle path were recorded and their characteristics related to the directional components of the interplanetary magnetic field and the level of geomagnetic activity, as these geomagnetic parameters play an important role in determining the state of the high-latitude ionosphere View full abstract»

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  • Frequency response of N-port planar gyromagnetic circuits using the mutual energy-finite element method

    Publication Year: 1997 , Page(s): 221 - 228
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The finite element method may be used to characterise reciprocal and nonreciprocal planar circuits in conjunction with a Green's function or a mutual energy formulation. While the former method has been used to describe both types of circuit, the latter has only been used so far to describe reciprocal ones. The purpose of the paper is to extend the mutual energy approach to the analysis of gyromagnetic circuits. The solution developed is demonstrated by analysing the operation of a 2-port gyromagnetic dipolar switch using a disk resonator. The results obtained in this manner are in good agreement with the mode matching approach View full abstract»

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  • Lattice Boltzmann method for wave propagation in urban microcells

    Publication Year: 1997 , Page(s): 251 - 255
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    A lattice Boltzmann model which simulates and predicts, on a massively parallel computer, wave propagation in urban environments is presented. This technique takes into account complicated boundary conditions. Two-dimensional simulations are performed starting from a city map and a renormalisation scheme is proposed to extend the results to three dimensions and adjust the wavelength. The method, which is simple and easy to implement, provides good path loss predictions when compared with in situ measurements View full abstract»

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  • Determination of dielectric distribution of a two-dimensional anisotropic cylinder with multilayer structure

    Publication Year: 1997 , Page(s): 229 - 234
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The algorithm for determining the dielectric distribution of a two-dimensional anisotropic cylindrical object is investigated using the unrelated illumination method along with the method of moments. In the study, a knowledge of the principal axes is no longer a prerequisite, which makes this scheme more attractive practically. Satisfactory reconstruction has been obtained for cylinders with off-principal axes. In addition, the influences of the noise level on the scheme are studied. The off-diagonal terms in the permittivity tensor are found to be more sensitive to the noise than are the diagonal terms. Therefore, they are the critical parts in obtaining good inversion. Finally, this scheme can now be applied to cylinders of arbitrary cross-section with a multilayer structure, for which the principal axes of each layer can be different View full abstract»

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  • Polygon subdomain basis-function model for the ring element in FSS arrays

    Publication Year: 1997 , Page(s): 209 - 214
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    An efficient subdomain approach is presented which can predict the frequency response of ring-element frequency-selective surfaces (FSS) more accurately than existing entire-domain models. The integral equation for the unknown fields (or currents) on the frequency-selective surface is used for the mathematical model, and the elements are approximated by two mutually rotated polygons. Roof-top basis functions are used on each polygon chord to represent the unknown fields (or currents). This method offers a significant improvement in computational efficiency when compared with other subdomain methods that have been reported. This is achieved by using far fewer subsections, thus reducing the number of unknowns to be determined. Numerical results for several FSS geometries are compared with those obtained using the entire-domain model and measurements, to demonstrate that this technique offers high reliability as a design tool, particularly for single-screen FSS structures View full abstract»

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  • Analysis of electromagnetic scattering by cylinders with edges using a hybrid moment method

    Publication Year: 1997 , Page(s): 235 - 240
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    The paper presents a method to improve the applicability of the fictitious source-model technique to metallic cylinders with sharp edges. Previous approaches have required that some of the fictitious currents be located in the proximity of the edges, so as to span the rapidly varying field in these regions. While success has been reported, the accuracy of these solutions has often been dependent on a judicious choice of source location. The fields in the vicinity of the edges are expanded in terms of analytical solutions of the infinite-wedge problem, while the field beyond these near-edge regions is expanded using fictitious current filaments. The operator equations, for the equivalent problem obtained in this manner, are imposed at the boundary between these regions. As the fields on this boundary are inherently slowly varying, the solution is less sensitive to the location of the fictitious current sources. Moreover, a higher accuracy in calculating the near-field quantities such as the induced surface current can be attained with a smaller number of expansion functions View full abstract»

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  • Improved numerical simulation of electromagnetic wave scattering from perfectly conducting random surfaces

    Publication Year: 1997 , Page(s): 256 - 260
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    A Monte Carlo simulation of electromagnetic scattering from one-dimensional perfectly conducting random surfaces is considered. Surface profiles of desired statistics are generated numerically using a standard procedure and the scattering solution for the surface samples of finite length is calculated using the method of moments. A new technique is used to reduce the effect of the edges of the finite surface samples. In this technique, the conductivities of the surface near edges are controlled by adding an appropriate tapered resistive sheet. It is shown that the accuracy at large angles of incidence, θ>50°, and the computation efficiency are improved significantly using this method, when compared to the standard tapered illumination method. Results based on this numerical approach are compared with those based on the small perturbation and physical optics approximations in their respective regions of validity View full abstract»

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