IEE National Conference on Antennas and Propagation
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- Location: York, UK
- Conference date: 31 March-1 April 1999
- ISBN: 0 85296 713 6
- Conference number: CP461
- The following topics were dealt with: urban propagation modelling for mobile radio; millimetre wave antennas; Earth space propagation; adaptive antennas for mobile communications; HF propagation; numerical techniques; wideband antennas; active antennas; propagation effects on fixed links; array antennas; multipath and diversity; ionospheric propagation; printed antennas
1 - 20 of 94 items found
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Printed fractal antennas
- Author(s): R. Breden and R.J. Langley
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One aspect of this paper is to describe the possibilities for reducing the overall size of a monopole so that they can be hidden within a system rather than protrude from it. Improved bandwidth results from the bow-tie monopole but there are instances where individual bands rather than a single band is preferable, for example for rejection of unwanted signals. One class of antenna to replace the monopole is the printed fractal antenna. Two types of fractal antennas are discussed, the Koch fractal patterns and the Sierpinski gasket which is akin to a printed bow-tie antenna. In both classes of antenna their radiation patterns, efficiency and frequency response as well as dimensions are discussed and compared. The principal application for the work described here is to provide hidden antennas on vehicles for multiband radio and television services. These include AM, FM and DAB services.
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Characteristics of a mid-latitude NVIS HF radio channel
- Author(s): S.J. Burgess and N.E. Evans
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This paper reports on the initial findings of measurements taken using a low cost, near vertical incidence skywave (NVIS) single channel sounder. The path investigated is unique in that although it is truly non-line-of-sight, operational results have been documented for coverage just beyond the ground-wave range; in the literature to date a commonly suggested NVIS lower boundary is 80 km. The consistency of the link reflects the potential of the NVIS technique for many practical short- to medium-range data communication scenarios, especially if store-and-forward techniques can be adopted.
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Short-term ionospheric forecasting over Europe
- Author(s): M.I. Dick ; M.F. Levy ; L.R. Cander ; I. Kutiev ; P. Muhtarov
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An operational forecasting tool for the European region based on continuous monitoring of the ionosphere is available on the World Wide Web for interactive use (http://www.rcru.rl.ac.uk/iono/maps.htm). A network of 23 ground-based vertical incidence ionosondes provides the basic inputs for the region of interest (10°W-90°E, 30°-70°N). Measurements of foF2 and M(3000)F2 are sent by e-mail, mainly in the form of URSIGRAM messages as described in ITU-R Recommendation P.313. Data are currently updated every 24 hours, though not all ionosondes provide values over the week-ends. Forecasts and archive measurement maps of the critical frequency foF2 and the maximum usable frequency for a 3000 km range, MUF(3000)F2, are then produced for the area of interest. Comparisons between the maps derived from measured and forecast values have been conducted.
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A staggered waveform HF frequency modulated radar simulation
- Author(s): S. Salous ; M. Musal ; M. Moorhead
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The use of three staggered waveforms with HF frequency modulated continuous waveform, (FMCW), radar is described in this paper. This technique is introduced to overcome the Doppler/range ambiguity problem usually associated with this type of radar. The waveforms are transmitted sequentially during a single target illumination time. The combination of the waveform repetition frequencies, (WRFs), are chosen to have a common multiple frequency greater than the expected target velocity to enable the resolution of the Doppler ambiguity. The simulated results show that this technique is useful in eliminating the effect of ambiguities caused by Doppler spread clutter or that caused by discrete signals of high Doppler targets.
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Bricks: a theorist's point of view
- Author(s): C.C. Constantinou ; M.J. Mehler ; C. Demetrescu
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In this paper we consider the question of how accurately we can model fields in the shadow regions of lossy dielectric canonical wedge-shaped objects. This is of particular importance in radio planning, since it is often necessary is calculate the field strength beyond a base-station's normal coverage area in order to determine carrier to interference ratios.
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A very fast ray-based field strength prediction tool for urban microcels operating in the UHF-band
- Author(s): J. Beyer and R. Jakoby
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Many microcell models in literature apply ray tracing or ray launching techniques, having however the disadvantage of consuming too much computer-running time for engineering applications. The number of propagation paths has to be minimised and the path finding algorithms have to be simplified in order to achieve a much faster average field strength prediction. This is possible particularly for dense urban microcells, where, in essence, street canyons can be assumed. On behalf of the Research Centre of Deutsche Telekom a prediction tool was developed based on this assumption and on two semi-empirical models to determine the propagation loss through these street canyons. To extract the empirical propagation parameters and to verify the fast prediction tool, comprehensive simultaneous measurements at 919 and 1873 MHz were carried out in many different streets and in two urban microcells of approximately 600×800 m.
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Modelling of handset antenna interactions with the user and SAR reduction techniques
- Author(s): S.V. Amos ; M.S. Smith ; D. Kitchener
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Today's mobile phones require proof of compliance to standard limits of the specific absorption rate (SAR), before they can be allowed onto the market. The SAR is a calculation of the power absorbed by tissue, averaged over a mass, resulting from the radiation of the handset. This requirement is set by standard committees worldwide making it a critical design consideration for the handset and antenna. The article presents an investigation which highlights how handset designs employing common elements such as the whip and PIFA (planar inverted F antenna) are very sensitive in their resulting SAR averages when alterations to the structures are included. It is seen that simple changes to the handset model can result in large improvements in the SAR performance.
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Model for wave propagation in presence of vegetation based on the UTD associating transmitted and lateral waves
- Author(s): R. Matschek ; B. Linot ; H. Sizun
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This paper presents several models of the literature applied to a wooded cross-road configuration in microcellular context at 1.9 GHz. A new UTD-based model is detailed, in which two modes of propagation are taken into account: direct and lateral waves. Simulations are compared with measurements.
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Analysis of wideband fading on UHF mobile radio channels
- Author(s): S. Salous and L. Bertel
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Frequency selective fading as a function of time was detected in wideband urban measurements carried out over a 90 MHz bandwidth at 1.8 GHz. A signal model based on optical geometry was used to interpret the results and as the basis of a simulation programme. The paper briefly discusses the model and the measurement system, and presents results from measurements and simulations.
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Outdoor-indoor wideband study for third generation communication systems
- Author(s): A.M. Street ; J.G.O. Moss ; A.P. Jenkins ; D.J. Edwards
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This paper reports a vector network analyzer based wideband radio channel measurement system that is configured for dual channel reception and employs an RF over fibre link to allow remote siting of the transmit antenna. A synthetic volume aperture is used to provide a full wave description of the channel and thus allow identification of multipath angle of arrival. The system is aimed at characterising indoor, indoor-outdoor and short range outdoor environments. Some results from an indoor-outdoor study pertaining to the behaviour of a W-CDMA system are presented to illustrate the power and versatility of the measurement technique.
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FSS array generation by optical means
- Author(s): D.S. Lockyer ; J.C. Vardaxoglou ; M.J. Kearney
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We have demonstrated a basic technique for optically generating arrays of periodic grids as a pseudo-metallic, electron-hole plasma region within a semiconductor wafer. The wafers used were high resistivity silicon to give dielectric-like dark behaviour, in order to contrast with the generated plasma. The theory of the work is based on the characterisation of the plasma by means of its surface impedance, which in turn is dependent on the complex permittivity. We have demonstrated theoretically, generation dimensions. Results have been presented in the frequency range 18-40 GHz to confirm that grids have been optically cast onto the wafers using negative image masks of the desired pattern.
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A millimetre wave reflector antenna for telematic applications
- Author(s): A.D. Searle ; R.A. Lewis ; B.P. Pirollo
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A shaped beam reflector antenna suitable for future telematic systems has been successfully demonstrated at 63 GHz. This has shown that reflector profile synthesis based on an aperture plane approach can be applied to highly shaped beams extending over wide angular regions. The antenna performance can be significantly modified by scattering from the feed and surrounding structures. These effects can be predicted by use of the FDTD method of analysis in place of a more conventional physical optics approach which neglects nearby dielectric bodies. This allows the investigation of antenna performance when installed in a wide range of locations on motor vehicles. Potential low cost manufacturing techniques have been identified and it is believed that a millimetre-wave reflector antenna could be economically viable for the consumer automotive market.
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Investigation of loaded microstrip patch antennas for wide-band mm-wave applications
- Author(s): E.E. Okon and C.W. Turner
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Results of an investigation into the enhancement of microstrip patch antenna bandwidth are presented. A resistive load is strategically coupled to the patch antenna in a two port configuration. Variation of coupling to the resonant patch yields bandwidths ranging from a few per cent to well over 60 per cent (VSWR2). This technique is then applied to a serial array of patch antennas. The series array is shown to improve the efficiency of the loaded patch antenna. Computed and measured results at X-band are in close agreement. Application is envisaged for wide-band mm-wave communications and radar.
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Comparison of reflection mechanisms from smooth and rough surfaces at 62 GHz
- Author(s): A. Hammoudeh ; J.-P. Pugliese ; M.G. Sanchez ; E. Grindrod
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Mobile broadband services (MBS) have been assigned frequency bands around 40 and 60 GHz and will allow wireless access at 155 Mb/s. Such services are expected to be delivered by systems operating in urban microcells employing low powered base stations with antennas which are elevated by a few meters above the ground. One technique that may be used to model the channel characteristics is ray-tracing. In a microcellular mobile radio channel the phases and amplitudes of the rays undergo some modifications when they are reflected from or transmitted through a particular material. Reflection and transmission mechanisms are dependent on the nature of the surface (smooth or rough), its dielectric parameters (permittivity and conductivity) and polarisation. The objective of the study reported is to measure and characterise the reflection mechanisms from smooth and rough building surfaces at 62.4 GHz. Results from experiments, made inside an anechoic chamber, on various smooth and rough building materials to measure the reflection and transmission coefficients as functions of the incident angle are given. A model based on multiple successive internal reflections inside the slab has been successfully used to describe these mechanisms for smooth surfaces with a thickness not too large compared to a wavelength. However results from rough surfaces, constructed by impregnating concrete slabs with angular stones, are compared with predictions obtained from the Kirchhoff approximation assuming random rough surfaces.
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Diurnal variations of 20 GHz and 40 GHz slant path attenuation statistics in southern England
- Author(s): S. Ventouras and C.L. Wrench
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Knowledge of the extent and occurrence of periods when high, and low, attenuation is most likely to occur along slant path links during a typical day is going to be important when planning the design, and use of, future slant path communication systems. This paper presents a statistical analysis of one years measured slant path propagation characteristics at 20 and 40 GHz in southern England; there is a special emphasis on the seasonal and diurnal variations of the attenuation statistics. In particular, the results presented will be of use to system planners who are seeking to make optimal use of low link margin satellite communication systems that incorporate EHF transmissions.
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MIDAS: a monthly link budget and signal coverage tool for frequencies between 10 and 50 GHz
- Author(s): A. Akram ; A. Shukla ; T. Konefal ; P. Watson
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Decision aid tools are becoming increasingly important for design, planning and deployment of mobile communications assets that must function in diverse global environments. A 10-50 GHz monthly, global prediction model has been developed that calculates signal attenuation and availability due to rain, clouds, water vapour (in rain and non-rain conditions) and oxygen. The model is a key element of the Millimetric Decision Aid System (MIDAS) tool being developed at DERA. MIDAS is currently used to provide monthly coverage maps of availability and attenuation, link margin-range trade-off maps and link budget analyses. The paper first describes the framework of MIDAS Version 1.0a. Prediction results from the tool are compared with measurements from a satellite path and a 37 km high altitude slant path. An airborne scenario is then analysed to show the signal coverage features of the tool.
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Frequency scaling factor of amplitude scintillation variance for satellite communication systems
- Author(s): C. Catalan ; B. Gremont ; E. Vilar
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This paper investigates the stochasticity of the instantaneous frequency scaling factor of the scintillation variance which is found to yield consistent values when compared with experimental work and can find direct application in the design of fade countermeasure systems.
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TLM investigation of dielectric-loaded bifilar personal telephone antennas
- Author(s): G. Nicolaidis ; O. Leisten ; J.C. Vardaxoglou
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Bifilar miniaturised antenna topologies combine good radiation and input impedance characteristics with regards to the design of personal telephones. In addition, ground-coupling effects are reduced and local to the body fields produce electric and magnetic minima. The current distribution is controlled in such a way that electromagnetic minima occur axially with the operator's body. At present, approximate analytical methods of this antenna geometry are not accurate for predicting the resonance frequency. The main purpose of this paper is to show the outcome of a thorough modelling investigation of the aforementioned antennas by displaying results of their radiative characteristics, as well as the current distribution and reactive fields. The antenna was analysed by means of a time domain transmission line modelling (TLM). This was implemented in package called MicroStripesTM produced by Kimberley Communications Consultants.
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Improved modelling of propagation and backscattering of millimetre waves in the melting layer
- Author(s): L. Raynaud ; I. Chenerie ; J. Lemorton
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The frequency bands, presently used by space telecommunications systems, are saturated, hence the need for using higher frequencies (EHF). However, for millimetre waves, the atmospheric propagation of electromagnetic waves is more perturbed than at lower bands. Precipitation, clouds and gases are responsible for that. The contribution of the melting layer, in terms of attenuation, is also no more negligible. This atmospheric layer, where ice particles melt into raindrops, still cause problems of characterisation and modelling. Furthermore, the melting layer can be responsible for the phenomenon of frost on the aircraft. Fortunately, this band can be easily detected because of its peak of reflectivity in the millimetre domain. It is for this reason that the melting layer is detected as a `bright band' by radar. This study deals with the characterisation and modelling of the melting layer in order to better predict its effects on the performance of spatial telecommunications systems in the EHF domain, and also to assess radar performance for melting layer detection at a distance. Some models already exist and are presented, but they are not entirely satisfactory. It is also for this reason that a new calculation for scattering by a particle is introduced. The results of simulations and a comparison with experimental data are presented.
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Simulation of a high frequency satellite link with a fade countermeasure
- Author(s): B.C. Gremont and M. Filip
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A DSP simulator of a full duplex high frequency satellite link with a generalized fade countermeasure has been presented. By feeding synthesized stochastic/dynamic rain attenuation and amplitude scintillation time-series into detailed power link budget equations, it is possible to simulate the expected carrier/noise ratio variations on either forward or return channels. Due to frequency scaling, these will in general be different even on a symmetrical VSAT network. The proposed fading simulator can mimic most known characteristics such as geographical diversity, instantaneous frequency scaling and hysteresis for rain attenuation. The communication channel simulator can match, in the long run, the expected long-term power spectral density and first order statistics as predicted from models. It is also emphasized that the use of a generalized fade countermeasure results in a very substantial improvement in user data throughput allowing operation close to channel capacity.
