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Antennas and Propagation, Tenth International Conference on (Conf. Publ. No. 436)

Date 14-17 Apr 1997

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  • Capacity increase in cellular radio networks using intelligent underlay overlay

    Publication Year: 1997 , Page(s): 119 - 122 vol.2
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    Intelligent underlay overlay, a network feature which enables significant capacity increases in digital cellular TDMA radio networks, is described. The capacity increase is obtained from existing `macro'-base station (BTS) sites since intelligent underlay overlay enables a more efficient utilisation of radio channels than currently possible. Theoretical principals and differences in functionality between intelligent underlay overlay and conventional underlay overlay are highlighted. In addition the aspect of dimensioning IUO cells is addressed View full abstract»

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  • Some observations of the directions of arrival of the Doppler components of an ionospherically reflected HF radio signal from Svalbard to the UK

    Publication Year: 1997 , Page(s): 67 - 70 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    Observations of the direction of arrival of a narrow band pulsed channel sounding signal propagated over a high latitude path have been made with a multichannel receiver system connected to a wide aperture antenna array. The signals received on each antenna were processed to provide a measure of the relative times of flight of the propagating modes and their associated Doppler spectra. In this way, the signal was split into complex amplitude components distinguished by the antenna position, time of flight and Doppler frequency. A direction finding algorithm was then applied to each of the signal components in turn in order to determine the directional characteristics of the received signal View full abstract»

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  • Application of the lattice gas automata technique to modelling wave interaction with biological media

    Publication Year: 1997 , Page(s): 286 - 289 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    We present a new computational electromagnetics technique based on the lattice gas automata approach and show how it can be applied to the simulation of electromagnetic wave interaction with biological systems. The numerical simulation of wave propagation and scattering in electromagnetics has almost universally been approached using a differential equation description of a problem. An alternative and relatively new computational electromagnetics approach are lattice gas automata. A lattice gas automaton (LGA) is an extremely large regular lattice of simple interconnected cells (a few bits per cell), with each cell of the lattice implementing the same simple rule. We have developed and demonstrated LGA algorithms for simulating a variety of electromagnetic propagation and scattering problems. We introduce new algorithms which enable the LGA approach to be used for modelling inhomogeneous dielectric media and show how these can be applied to modelling field interaction with biological systems View full abstract»

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  • Determination of HF ray path parameters using a multi-quasiparabolic model ionosphere

    Publication Year: 1997 , Page(s): 23 - 26 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    The multi-quasiparabolic (QP) model ionosphere has become available with the desirable features of providing explicit oblique ray path analytic expressions for ground range, reflection height and phase path, etc. at HF radio frequencies. The need for time-consuming numeric ray tracing is reduced. Electron density profiles are synthesised as combinations of QP and inverted QP segments to provide a match to any desired accuracy by changing the number of chosen segments. A family of different profiles parametric in terms of standard scaled vertical-incidence ionospheric characteristics has been simulated in this way for any location and time-of-day View full abstract»

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  • The statistics of propagation on the 500 m millimetre wave experiment at Chilbolton

    Publication Year: 1997 , Page(s): 374 - 377 vol.2
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The rapid and continuing expansion in communications is imposing ever-increasing demands on the electromagnetic spectrum, which, although a reusable resource, is becoming over populated, giving rise to additional problems such as interference between adjacent channels and restricted bandwidth (and therefore channel capacity). There is a need to develop communications systems to higher frequencies, extending into the millimetre wavelength regions of the electromagnetic spectrum. The results of a preliminary statistical analysis of propagation conditions obtained during 1993 on the 500 m millimetre wave experimental range at Chilbolton are presented. Examples are given of studies in rainfall attenuation and total attenuation including worst month analysis. The 500 m range comprises a set of single-pass, continuous-wave (CW) transmission links, situated 4 m above flat grassland, operating at frequencies of 57 GHz, 97 GHz, 135 GHz and 210 GHz, with vertical polarization, and at wavelengths of 10.6 μm in the infrared and 0.63 μm in the optical wavebands, with random polarization View full abstract»

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  • An improved three-dimensional propagation model and measurements for indoor wireless communication systems

    Publication Year: 1997 , Page(s): 316 - 318 vol.2
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    An improved three-dimensional ray tracing propagation model based on multiple-image and ray launching concepts is presented. The model yields large improvements in terms of accuracy and computing efficiency compared with the conventional “brute force” ray tracing method. Calculations are compared with measurements in an indoor environment View full abstract»

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  • A comprehensive/selective mm-wave satellite downlink experiment on fade dynamics

    Publication Year: 1997 , Page(s): 98 - 101 vol.2
    Cited by:  Papers (1)  |  Patents (100)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The paper gives a succinct but comprehensive overview of an experimental set-up, salient features and initial results of a satellite downlink propagation experiment at 40 GHz and referred to propagation and communication-related results. The global objective of the research aims at a better understanding of dynamic fading and C/N0 ratios, whether due to cloud attenuation and its variability, or to rain plus tropospheric (clear air) scintillations and sky temperature fluctuations View full abstract»

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  • Some super-resolution DF measurements within the HF band

    Publication Year: 1997 , Page(s): 71 - 74 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The unknown propagation mode content of signals monitored in some earlier super-resolution HF-DF experiments was a significant limitation in the interpretation of the measurements and inferences concerning the mode content had to be made from the processed data. In order to overcome this limitation, further experiments have been undertaken in which the propagation mode content of the signals was determined by oblique sounding. Measurements made over a 778 km path from Wick, Caithness to Cricklade, Wiltshire are reported. The complex amplitude distributions of the received signals were sampled by means of a wide aperture multi-element antenna array connected to a 6-channel receiving and data recording system. The directions of arrival were subsequently estimated by applying various super-resolution direction finding algorithms to the recorded data. Two super-resolution algorithms were employed in these studies: (a) the MUSIC algorithm and (b) an iterative null steering technique based on the IMP algorithm and the DOSE algorithm. Enhancements have been made to the null steering algorithm and a description of the modified algorithm is given View full abstract»

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  • Analysis of mobile-satellite propagation measurements at 18.7 GHz: vegetation effects

    Publication Year: 1997 , Page(s): 9 - 14 vol.2
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    Some measurements in the Ka band (at 18.7 GHz) on a land mobile satellite propagation link (ITALSAT 13.2° EST) have been analyzed. These measurements have been performed in surrounding areas of Turin, in the period between February and December 1995, Italy, using the ESA Land Mobile Beacon Terminal (LMBT). ITALSAT is seen from Turin with an elevation angle of 38.7° and an azimuth angle of 172.3°; its 18.7 GHz beacon has a reduced coverage, but nevertheless in Turin and with the LMBT instrumentation, the dynamic range of the received signal is approximately 22 dB. The main targets of the work, carried out on sites with only buildings or vegetation, have been the statistical characterization of the Ka mobile channel in different environments (urban, suburban, highway, open areas) by dynamic measurements, and the validation of a geometrical model for vegetation, developed in CSELT, through static measurements. In fact we have evaluated the attenuation due to different vegetation depths by a series of measurements effected with the van parked, in the surroundings of the town: the target of the analysis of these static measurements has been to validate the ITU-R model, at 18.7 GHz, and eventually to give some suggestions for a further improvement. Furthermore, to make easier the study of the measurements and of the causes that generated the attenuation, a Multimedial Analysis of Data System (MAD), that makes it possible to compare simultaneously the radioelectrical parameters and the visual ones taken by two video cameras, has been developed in CSELT View full abstract»

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  • Experimental study of radiowave propagation effects in the millimetre-wave band

    Publication Year: 1997 , Page(s): 387 - 390 vol.2
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    This paper deals with the CELESTE experiment which is dedicated to the assessment of propagation effects observed in the EHF band (34.5 GHz) on a low-elevation path. These effects are principally due to absorption and scattering by raindrops, but also by atmospheric gases (mainly H2O and O2) and particles in clouds, and lead essentially to attenuation and depolarisation of the wave along the path. The main objectives of this experiment are first explained and then the current experimental set-up and its future evolution are described. The paper also reports on the statistical analysis of radiowave and rain data: the comparison with various prediction models indicates that the measured attenuation distributions are largely below the predicted ones for time percentages less than 0.1% View full abstract»

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  • Linear polarisation-diversity radar estimation of apparent canting angle of raindrops

    Publication Year: 1997 , Page(s): 339 - 342 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    We report a newly developed algorithm to estimate the apparent canting angle of raindrops from a linear polarisation-diversity radar system. Based on the dependence of linear depolarisation ratio on the canting angle and attenuation, an estimator for the apparent canting angle of raindrops has been derived, in which the size of canting angle can be directly estimated from linear polarisation-diversity radar measurements. Radar data from the S-band Chilbolton Advanced Meteorological Radar (CAMRa) are used to demonstrate this estimator View full abstract»

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  • Diffraction of an electromagnetic wave on a flat periodic structure

    Publication Year: 1997 , Page(s): 239 - 242 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The authors use a flat periodic structure to represent a half-infinite dielectric layer with complex dielectric permeability on which are located metal bars. EM diffraction by this system and losses are discussed View full abstract»

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  • Radiowave propagation over irregular terrain using the 3D parabolic equation

    Publication Year: 1997 , Page(s): 359 - 362 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    The authors develop a radiowave propagation prediction model suitable for use over irregular terrain in the VHF and UHF bands. Existing models are predominantly 2D and therefore take no account of terrain gradients transverse to the great circle path, obstacles to the side of the great circle path (such as hills) or propagation around the sides of obstacles. Their aim is to reduce these errors by developing a model which incorporates the 3D nature of the terrain. Many existing propagation prediction models use an idealised knife-edge representation of the terrain and this gross simplification is known to lead to large errors in certain situations. The parabolic equation (PE) method uses a more accurate representation of the terrain, as well as incorporating the surface impedance of the terrain View full abstract»

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  • Measurements of non line-of-sight VHF propagation over the sea surface

    Publication Year: 1997 , Page(s): 378 - 380 vol.2
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    On two occasions in 1994, a set of trials were carried out to measure the signal strength as a function of the range between three vertically-polarised floating transmitters, operating at frequencies in the VHF band, and a ship-mounted receiver. The trials corresponded to sea states from 2 to 5, and ranges up to 30 Nautical miles (1 Nm=1852 m), beyond line of sight of the transmitter. The paper describes the variation of signal strength as a function of the range and sea state. A literature search suggested that very little has been published on this kind of propagation. The paper derives the equations to extrapolate the data from the received power vs. range curves, in order to determine the variation of signal strength with the range, and to study its variability with the sea state View full abstract»

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  • HF transmitter SSL (single site location) with combined ionospheric update

    Publication Year: 1997 , Page(s): 63 - 66 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    HF-SSL is a useful technique for identifying the location of HF transmitters when information is only available from a single site. The main source of error in the technique has generally been found to be an inability to model in sufficiently accurate detail the ionospheric effects on the signal propagation which require accurate characterisation of the ionosphere at the time of observation. The method presented reduces errors from this source by using a Nelder-Mead (1965) function minimisation algorithm to produce an optimised solution for a real-time updated ionosphere mode as well as the HF transmitter location. The method can be applied to the situation where two simultaneous paths exist from the transmitter to receiver, e.g. 1E and 1F2 or 1F2 and 2F2. This is a condition which is often satisfied and it has been found that super-resolution methods can be used to successfully decompose the received HF wavefield, received on a suitable antenna array, into its constituent component giving the DOA of each. Thus such a scheme compliments more traditional SSL methods using interferometry which are often only performed for single mode propagation. Further, in the extended method, measured angles of inclination to known transmitters and differential time delays between modes can also be employed in the optimisation, producing a more accurate estimate of both the ionosphere model and propagation distance View full abstract»

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  • Attenuation statistics of non rainy atmosphere at 20-30 GHz

    Publication Year: 1997 , Page(s): 149 - 152 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    In the frequency bands above 20 GHz, in non-precipitating conditions, the atmospheric components relevant to radiowave propagation are oxygen, water vapour and the liquid droplets of clouds. Whilst cloud absorption increases with frequency, gases present absorption peaks, around 22 GHz and 60 GHz for water vapour and oxygen, respectively. These features have an impact on those satcom systems, such as commercial VSATs and business direct access terminals, where the power margin is reduced and the adoption of sophisticated countermeasures is limited by dimensions and cost effectiveness. The results are presented of the experimental campaign carried out with a dual-channel 20/30 GHz radiometer at Roma, Italy, along four years, September 1992-August 1996. Statistics are produced of zenith atmospheric attenuation in non-rainy conditions on a yearly basis, as well as for average seasons, months and hours of the day, from which the expected attenuation can be observed. Careful analysis is also focused on the two separate contributions of water vapour and cloud liquid View full abstract»

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  • Propagation measurements using ITALSAT beacons together with associated measurements of radar reflectivity from rain and clouds at 3 GHz and 35 GHz

    Publication Year: 1997 , Page(s): 102 - 105 vol.2
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    This paper gives some preliminary analyses of beacon measurements near 40 and 50 GHz in comparison with radar soundings at both 3 and 35 GHz along the path to the satellite. Two events are analysed, one occurred on 19/9/96 and the other on 30/9/96. This work forms part of a general programme to evaluate the effects of rain, cloud and atmospheric gases on radiowave propagation along Earth-space paths in the 30 to 50 GHz band. It constitutes an extension of the results presented at 1CAP'95 by Ventouras et al. (see ICAP'95, IEE Conf. Pub.407, p.27-31) for the 12 to 30 GHz band using emissions from the Olympus satellite. The investigations in the higher band, particularly for 40 to 50 GHz, place considerably more emphasis on the attenuation caused by cloud and gas since this is important for systems operating with small fade margins. A video cloud camera and an instrument to measure the height of the cloud base have been regularly employed in conjunction with the beacon receivers and meteorological equipment. A multi-parameter radar has been used to derive concurrent information on the atmospheric constituents for selected periods View full abstract»

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  • Analysis of UHF propagation in a city street modeled as a random multislit waveguide

    Publication Year: 1997 , Page(s): 214 - 217 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    Attempts to reduce the interference level and consequently increase the spectral efficiency of the cellular radio communication systems require the lowering of antenna heights. In large metropolitan areas having high buildings such a requirement leads to a situation where the transmitting and receiving antennas are both located below the rooftops and the city street acts as a type of a waveguiding channel for the propagating signal. In order to optimize the design of the local communication networks there is a need to develop efficient algorithms for computation and mapping of the field distribution in such structures. We apply the waveguide model for a city street with irregularly spaced high buildings by employing ray-optical methods. This approach allows us to compute not only the variations of the energetic parameters of the field along the city street but also to present analytical expressions for the spatial structure of the field and to account in the future for the influence of the roughness of the walls and scattering by trees and other obstacles View full abstract»

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  • A recursive model for the field strength prediction with neural networks

    Publication Year: 1997 , Page(s): 174 - 177 vol.2
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    A new model for the field strength prediction for mobile communication networks inside buildings is presented. The model consists of a neural network, trained with measurements and combines the advantages of empirical models (short computation time) with the advantages of deterministic models (waveguiding). The prediction results compare favourably with measurements View full abstract»

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  • HF guidance in the vicinity of F layer maximum during ionospheric disturbances

    Publication Year: 1997 , Page(s): 265 - 268 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    In the regular ionosphere the main characteristics of short wave propagation are described by the geometric-optic approach and have been studied sufficiently well. The existence of irregularities and disturbances of different forms complicates the propagation picture determining the scattering and diffraction effects. Despite widespread investigations of ionosphere irregular structure and its influence on radioelectronic systems the role of irregularities in ionospheric propagation has not yet been established fully. In the report experiments on oblique chirp sounding of the ionosphere, where the guidance effect of the Pedersen mode in the disturbed ionosphere was discovered, are presented. A theoretical explanation of the observed phenomenon is given and opportunities for the use of this effect for diagnostics of irregular structure in the ionosphere are also discussed View full abstract»

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  • Electromagnetic field penetration through small apertures in a room

    Publication Year: 1997 , Page(s): 277 - 280 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    This paper presents a finite-difference time-domain (FDTD) formalism allowing one to model small apertures without discretization. This formulation is based on Bethe's small hole theory, which approximates the fields diffracted by a small aperture as equivalent to the fields radiated by an electric and a magnetic dipole. In the model, the analytical fields radiated by these two dipoles are discretized using the classical finite-difference scheme. The model is then validated by comparing it with exact FDTD. Applications and an extension of the model allowing one to consider several apertures close to each other are also presented View full abstract»

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  • Predictive fade countermeasures for Ka band satellite systems

    Publication Year: 1997 , Page(s): 109 - 114 vol.2
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    This paper investigates the performance of a predictive fade control strategy based on a minimum variance approach for application to low fade margin Ka band satellite systems. Ideal beacon detection is assumed. A statistical model based on a modified concept of global fading process is developed. This is used to evaluate the performance of the fixed detection margin approach to account for scintillation-induced effects. This is expressed in terms of fade countermeasure (FCM) utilisation ratio. The impact of time delays on the design and performance of an adaptive transmission rate countermeasure is also evaluated View full abstract»

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  • Performance characterisation of millimetre wave mobile radio systems in forests

    Publication Year: 1997 , Page(s): 391 - 396 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The frequencies in the oxygen absorption band in the region of 60 GHz have been suggested for urban microcellular communications. This is due to the extra attenuation exhibited by the atmosphere in this frequency region, thus allowing for greater frequency re-use to be employed. Multipath in a microcellular forest environment due to reflections and scatter off foliage, with line-of-sight (LOS) prevailing, has not been examined. This study evaluates the severity of multipath in a mobile radio microcellular forest channel due to the presence of foliage. A number of measurements have been made at 62.4 GHz in the Forest of Dean, to evaluate the performance of millimetric cellular mobile radio communications for military applications. Measurements have been made by transmitting a continuous wave (CW) signal from a fixed base to a mobile receiver, and recording the signal envelope variation as a function of mobile position. The results of the propagation experiments are presented. Cumulative distribution functions for the received signal envelopes, as well as corresponding power spectra, are shown and described. A simple ray model is developed to assist in interpreting the experimental results obtained in this type of environment View full abstract»

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  • An extended propagation software package for indoor communication systems

    Publication Year: 1997 , Page(s): 298 - 301 vol.2
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    At the K.U. Leuven a software package (EPICS) that uses deterministic models to calculate the fields of antenna arrays has been developed. The software also allows one to compute important parameters of communication system like the power delay profile (PDP) and direction of arrival (DOA). Originally, it was designed to evaluate outdoor communication systems, but the emphasis has been moved towards the smaller and more difficult environments of indoor propagation. For outdoor communication the model was based only on three-dimensional physical optics (including diffuse scattering) reflection phenomena. This model has been extended by introducing penetration through walls and the uniform theory of diffraction (UTD). Also, new formulas containing Fresnel integrals and allowing closer distances between the reflecting surface and the receiver or transmitter were developed and introduced. These three aspects are also discussed View full abstract»

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  • Scattering and extinction: dependence upon raindrop size distribution in temperate (Barcelona) and tropical (Belem) regions

    Publication Year: 1997 , Page(s): 230 - 233 vol.2
    Cited by:  Papers (4)  |  Patents (100)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    This paper gives a summary of the salient results derived from experimental campaigns carried out in Belem and Barcelona in 1994. The instrumentation used is briefly described. The research shows that there was no significant differences in raindrop size distribution N(D,R) between the two sites. Both log-normal and gamma distributions are adequate to model the distributions. The N(D,R)-based equivalent radar reflectivity and specific attenuation are given and compared with literature results View full abstract»

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