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Microwaves, Antennas and Propagation, IEE Proceedings H

Issue 5 • Date Oct 1993

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Displaying Results 1 - 18 of 18
  • Quadruple-site diversity experiment in Austria using 12 GHz radiometers

    Page(s): 354 - 360
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The paper reports on a quadruple-site diversity experiment using 12 GHz radiometers in Austria. Separations between sites were 10.9 to 26.2 km, providing orthogonal path separations (vertical or horizontal) of between 9.3 and 25.9 km. The radiometers were directed along the future look-angle of the ESA satellite OLYMPUS (azimuth 223.16° from true North, elevation 25.43°). The measurements were conducted from May 1980 to April 1983, with dual-site joint uptimes exceeding 94.9% for all combinations. The experimental results indicate that, for this location and geometry, dual-site diversity performance is insensitive to separations above 10 km, all pairs achieving similar diversity gain statistics. The results were close to those predicted by the Hodge model, with the prevailing weather direction having a significant influence on diversity performance. In general triple- and quadruple-site groupings provided better improvement in diversity than the dual-site combinations but, while the statistical improvement was slight, the number of joint events was significantly reduced from dual-site combinations View full abstract»

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  • Lossless transmission and the measurement of insertion loss

    Page(s): 390 - 394
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    A method of finding the true insertion loss of a dissipationless device interposed between a mismatched source and load is described. The VSWRs of the source, device, and load are found from the extremes, or in practice from the ratios of the extremes in transmission brought about by varying the electrical length of the interconnecting lines. The theory is verified by results obtained using a waveguide system with phase changers. A possible application would be in millimetre wave beam transmission where, in principal, only the source and detector need be moved to carry out the measurement View full abstract»

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  • Effect of multipath fading on millimetre wave propagation: a field study

    Page(s): 343 - 346
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    Analysis of clear air fading encountered on millimetric wave and infrared radio links are presented. The analysis is based on data obtained during a four-year field study in the city of Riyadh, Saudi Arabia. The region can be considered as a typical arid climate where the rate of evaporation is higher than the rate of precipitation. Maximum rain rate is of the order of 30 mm/h for 0.001% of the year. A brief description of the experimental setup is presented, together with the results of measuring clear air fading experienced by the radio links. Statistical characterisation of fading is given for both the millimetric wave links operating near 40 GHz and the infrared radio link at a wavelength of 0.88 μm. It is shown that fading is dominated by multipath, having a Rayleigh amplitude distribution and an occurrence factor similar to the microwave band. Fades were highly correlated for the two links sharing the same path and separated in frequency by 1%. Multipath fading was also measured on the infrared link. Even at the short hop length at 0.75 km, the occurrence factor was about 1%. Time duration of fades are also analysed, and fade durations were essentially exponentially distributed. Small fades, however, have normal duration distribution View full abstract»

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  • Studies of edge current densities in regular and superconducting microstrip lines of finite thickness

    Page(s): 361 - 366
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    Distributions of the current and the surface fields close to the corners of a conducting strip with rectangular cross-section are investigated by an accurate and efficient moment method. The strip is made of either a normal conductor or a superconducting material. Based upon this study, a simple graphical procedure for a rough estimation of the finite maxima of the current densities at the edges (corners) is presented View full abstract»

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  • Antenna testing from phaseless measurements: probe compensation and experimental results in the cylindrical case

    Page(s): 395 - 400
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The experimental feasibility of testing a radiating source by a method requiring only amplitude data is shown in the cylindrical scanning technique. The proposed innovative approach is applied to a set of measured near field data of a parabolic reflector antenna. The presence of a real probe antenna is also considered. No a priori assumption about the missing phase information is required; the solution is found by starting from a completely random first guess. The applied technique, especially at millimeter wavelengths, provides a powerful tool for dealing with several applications, such as f.i. reflector or array testing and diagnostics. It has high precision and employs less expensive and simpler setups View full abstract»

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  • Compact broadband TE01-mode generator

    Page(s): 339 - 342
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    A compact broadband TE01-mode generator is presented. It consists of five identical sectorial waveguides which are stepped into an ordinary circular waveguide. These sectorial waveguides are fed by five identical probes at the end of a star-shaped feed line with five arms. This feed line is placed in a trace between the sectorial waveguides. A consequence of the five-fold symmetry is that the lowest parasitic mode which can be generated and propagated has a cutoff far above the frequency range of operation (9.5-10.5 GHz). The measurements show that the return loss is less than -15 dB in the frequency range of operation. The mode purity is better than 99.4% View full abstract»

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  • Convoluted frequency-selective array elements derived from linear and crossed dipoles

    Page(s): 378 - 380
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    The development of a range of convoluted elements derived from linear and crossed dipoles is traced and their performance is examined experimentally and analytically in relation to their application to frequency-selective surfaces. These configurations give highly packed structures for use on curved surfaces or where maximum separation from the onset of grating responses is required. Two potential methods of analysis are a Floquet modal approach and a spectral iteration. Current distributions on an illustrative example are given. Calculated transmission responses of a convoluted dipole containing three cycles agree well with experiment View full abstract»

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  • Effect of parasitic dielectric resonators on CPW/aperture-coupled dielectric resonator antennas

    Page(s): 336 - 338
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    The effects of parasitic dielectric resonators on the HE11δ and HE13δ modes of a cylindrical dielectric resonator antenna (DRA) have been studied. The DRA was excited electromagnetically with a grounded coplanar waveguide through an aperture in the common ground plane. Strong couplings were observed for the HE11δ mode with the parasitic element superimposed on the driven DRA, and for the HE13δ mode with parasitic elements placed on both sides of the driven DRA. Results indicate significant enhancement in bandwidth for both modes, and good radiation patterns for the HE11δ mode View full abstract»

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  • One-point feed printed crossed dipole with a reflector antenna combined with a reactively loaded parasitic loop for land mobile satellite communication antennas

    Page(s): 417 - 420
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    A one-point feed printed crossed dipole with a reflector antenna combined with a reactively loaded parasitic loop is proposed. The parasitic loop contributes mainly to the improvement of the antenna gain, and the reactive loads contribute mainly to the improvement of the frequency response of axial ratio. Using the proposed antenna, a 4-element printed array antenna is constructed for land mobile satellite communications to obtain highly efficient, compact, light weight array antenna View full abstract»

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  • Analytic solution for TE-mode radiation from a flanged parallel-plate waveguide

    Page(s): 387 - 389
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    The problem of TE-mode radiation from a flanged parallel-plate waveguide is reexamined. The technique of the Fourier transform is used to represent the radiation field in a simple analytic series form. The series solution is compared with other results, thus clarifying the discrepancies between different numerical approaches. The analytic series solution is exact and more efficient than other existing numerical solutions View full abstract»

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  • Modifications to the theory of waveguide horns

    Page(s): 381 - 386
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    Waveguide horns have been extensively analysed by many authors, with broad agreement between the results of the various theoretical approaches, for medium- and high-gain horns. However, the approximations used in the calculation of the aperture fields are inaccurate when applied to low-gain horns, leading to errors in the calculated gain. A modified analysis is described, avoiding the most commonly used approximations. Experimental measurements on a 12 dB horn are used to substantiate the theory View full abstract»

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  • Optimisation of the coupled-mode method for the analysis of waveguides partially filled with dielectrics of high permittivity: Application to the study of discontinuities

    Page(s): 401 - 406
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    The differences between two distinct formulations of the coupled-mode method are analysed and justified. The difference, the mathematical basis of which is the different ways used to calculate the axial components of the electromagnetic field, is interpreted in terms of the continuity of the functions that affect the calculation of these components. The original formulation of the coupled-modes method is shown to converge in a more efficient way than the Ogusu formulation, although it is less efficient from a numerical viewpoint. Results of the propagation constant in isotropic dielectric waveguides are presented which confirm the better convergence of the original formulation. Applying this formulation in conjunction with the modal matching method allows an improvement in the accuracy of the analysis of dielectric discontinuities between materials of high permittivity. Then, this formulation is useful for designing isotropic dielectric structures as mode launchers or filters, as well as nonreciprocal elements constructed with ferrites View full abstract»

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  • Analysis of the effects of septum thickness on impedance and fields of TEM mode inside an asymmetric TEM cell

    Page(s): 347 - 353
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    Investigations have been carried out on the nature of variation of characteristic impedance of the TEM cell as a function of thickness and width of the septum for its different offset positions. The impedance is calculated by finding energy storage and power loss inside the cell, using Green's functions. Variations in characteristic and wave impedances with frequency of operation are also shown. The electric field distribution in the cross-section for different offset positions of the septum are also investigated and represented graphically View full abstract»

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  • Tchebyshev approximation method for Salisbury screen design

    Page(s): 414 - 416
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    Alternative responses of Tchebyshev approximation are presented for designing a screen based on the analytical formulas for the multiple electric and magnetic Salisbury screen. This screen has provided an increase in bandwidth over the known maximally flat responses. Both the Tchebyshev and maximally flat designs are applied to a multilayer screen, which include appropriate values for spacer materials and screen properties for analysing the screen reflection properties View full abstract»

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  • Experimental characterisation of UHF radiowave propagation through forests

    Page(s): 329 - 335
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    An experimental measurements programme for characterisation of radiowave propagation at UHF band is discussed. Preliminary results on transmission loss, specific attenuation and delay spread are presented and discussed in terms of the biophysical and radio parameters that characterise the propagation path. The results are compared with predictions based on discrete random medium model View full abstract»

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  • Radar cross-section of dielectric-coated conducting cylinder loaded with periodic metallic strips using mixed SDM, CGM and FFT:TE incidence

    Page(s): 373 - 377
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    A mixed technique is presented for calculating the radar cross-section characteristics of a dielectric-coated conducting cylinder with TE-wave incidence loaded with periodic metallic strips. The technique is based on the spectral-domain method (SDM), conjugate gradient method (CGM) and fast Fourier transform (FFT). Since the property of circular Toeplitz matrix has been used, only memory directly proportional to NsNb (Ns is the number of strips and Nb is the number of basis functions for approximating the currents on the strips) is needed, which allows treatment of the cylinder loaded with tens or even hundreds of strips. The RCS of a dielectric-coated conducting cylinder loaded with many periodic metallic strips are first calculated. Numerical results show that the RCS can be effectively controlled by adjusting the period or the spaces between strips View full abstract»

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  • Admittance characteristics of narrow radiating slots in nonradiating dielectric waveguide

    Page(s): 407 - 413
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    A study of an inclined slot cut in the metal wall of nonradiative dielectric (NRD) waveguide is presented. The modal expansion method is applied to the development of an equivalent network of a slot discontinuity in NRD waveguide, using the reciprocity and Poynting theorems. The effect of the metal wall thickness is taken into consideration by applying microwave network analysis. Numerical data for the normalised slot admittance is obtained and compared with experimental results. Good agreement is observed. Numerical data for the slot admittance for various dielectric materials is also presented and the radiation patterns of a single slot are included View full abstract»

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  • Holographic prediction of ground multipath parameters from range gain patterns

    Page(s): 367 - 372
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    A new technique is presented where the range gain pattern produced by ground multipath interference is considered as a hologram. The technique can be applied to both flat and spherical earth models. Field distribution at the transmitting antenna side is obtained by digital reconstruction from the range gain pattern. Transmitting antenna height and ground reflection coefficient can therefore be predicted. The technique is validated by calculated and measured range gain patterns, and the predicted values are in good agreement with actual ones View full abstract»

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