This book, and the lecture course on which it is based, is intended to deal with the practical engineering aspects of radiowave propagation, emphasising the propagation concerns and models and the associated prediction procedures which are appropriate for the system applications of current interest. For many years, a Radiocommunication Study Group of the International Telecommunication Union (ITU) has been studying propagation on a world wide basis and producing the Recommendations which give descriptions and prediction techniques for the propagation of radiowaves. These Recommendations are regularly reviewed and revised by international experts in ITU-R Study Group 3 and probably represent the latest and best tools which the engineer may use. The course deals with a number of these Recommendations.

Although for many purposes a radiowave can be treated simply as a power flow, there are other situations where it is necessary to take into account the fact that it consists of vector fields. Multiple radio paths (or rays) between a transmitter and a receiver can occur for various reasons, such as the combination of ground and sky waves, multimode sky-wave propagation, atmospheric refraction and layer reflection, and reflections from the ground and objects such as buildings. It is called multipath propagation, and can give rise to several effects on the received signal. A simple mathematical approximation which is widely used in radiowave propagation concerns situations where a right-angled triangle is long and thin, i.e. the hypotenuse is only slightly longer than one of the other sides.

This chapter introduces the principles of electromagnetic theory which are essential to an understanding of radiowave propagation. Where possible, a practical engineering approach has been adopted. However, the material has been structured to provide those with a more mathematical background with a satisfactory account of the subject, together with references to further reading material. Initially, propagation between two antennas in free space is considered by means of power flux concepts. This enables important ideas such as free-space path loss, antenna gain and effective aperture to be introduced. Maxwell's equations are presented. and plane-wave solutions are derived as a means of introducing polarisation, wave impedance and electromagnetic power flow. Finally, radiation from a current distribution is examined and illustrated by deriving the fields of a dipole antenna.

This chapter considers the effects of refractive index variations on the propagation of radiowaves in the troposphere, and in particular those mechanisms which lead to propagation beyond the normal line of sight. Clear air implies that the effects of condensed water (clouds, rain etc.) are ignored, although gaseous absorption is included. The frequencies of interest are above about 100 MHz; below this frequency refractive index variations are not strong enough to cause significant effects, and the ground wave and ionospheric mechanisms dominate at transhorizon ranges. The emphasis is on the meteorological mechanisms that give rise to anomalous propagation, and the basic models that have been developed to predict the effects of refractive index variations on radiowave propagation.

Short-range radio systems are used for many purposes for telemetry, remote control and games, as well as for communications. Communications uses include cordless telephony, radio local area networks (RLANs), radio fixed access and microcellular systems. For some of these applications, very low powers are used, with poor and poorly located antennas where the user only expects the range to be of the order of a few metres. For example, for remote car door locks, the user will expect to point the transmitter towards the car and probably has some understanding of the need to provide a near line-of-sight path. For such appli cations there seems to be very little requirement to attempt to provide good propagation models. For RLANs and other indoor applications there will be a need for some kind of generic modelling of the effects of the room size and shape, obstructions in the room, the construction materials and the penetration through walls and floors. For high-speed data transmission, it may also be necessary to model the multipath time spreads. But for outdoor microcellular systems and similar applications it will be necessary to model propagation at distances ranging out to a kilometre or so, where the longer-range area coverage prediction methods may take over. 1 km is the dividing distance used by the ITU-R in its Recommendations between short-range and longer-range prediction methods. However, the above considerations mainly apply to VHF and UHF systems, where although the distances are short the propagation is in the far-field regime and the usual propagation techniques are applicable. Another interpretation of short range would be to consider paths within the near field regime around the transmitting antenna. This is mainly of significance at lower frequencies.

This chapter describes key modelling concepts for mobile communication systems operated in outdoor environments.

Broadcasting is defined in the ITU Radio Regulations as 'a radiocommunication service in which the transmissions are intended for direct reception by the general public'. European broadcasting at VHF and UHF takes place in the frequency ranges shown in Figure 13.1. In the UK, 88-108 MHz is used for FM radio, 218-230 MHz is used for digital radio and 470-860 MHz is used for analogue and digital television.

This chapter discusses basic concepts regarding ionospheric electromagnetic wave propagation.

The ionosphere (the ionised region of the atmosphere between about 60 km and 1000 km) affects all radio signals below ~5 GHz which pass through or travel via it. Some of the associated radio systems can only operate because of the ionosphere, but it can also degrade radio system operation. Sometimes the effects of the ionosphere are highly significant, sometimes they can all but be ignored. For high-frequency (HF) sky-wave propagation, the ionosphere is, of course, a prerequisite. If the ionosphere were stable in time and constant in space, it would be relatively easy to determine the effect of the ionisation on the radio propagation and hence on the radio system. Unfortunately, stability is not the norm, particularly in the high-latitude regions, and, as a consequence ionospheric, prediction methods and models are required to support system design, service planning and frequency management. These methods and models characterise the medium and estimate the system performance. Some operate in real (or close to real) time and they may even directly advise the radio operator on a course of action which would improve system performance.

Recommendation ITU-R R530 (1999) presents propagation data for planning terrestrial line-of-sight radio systems, typically operating in frequency bands between 1 GHz and 45 GHz, and gives step-by-step methods for predicting the performance of these systems for percentage times down to 0.001 per cent. The recommendation deals only with effects related to the wanted signal. The interference aspects of terrestrial line-of-sight link design are covered in Recommendation ITU-R P.452 (1999). Although the prediction methods presented in Recommendation ITU-R P.530 are based on the physics of radio propagation, measured data was used as the main foundation and the majority of the formulae are semi-empirical statistical relationships. The Recommendation divides broadly into methods for determining the antenna heights (with and without antenna height diversity) and methods for calculating the statistics of signal fading, enhancement and depolarisation. In the case of clear air effects the methods are subdivided into a quick (initial planning) method and a more detailed method, which requires terrain data for the area of the link. Other topics covered are: the correlation of simultaneous fading on multihop links, the frequency and polarisation scaling of rain attenuation statistics, the statistics of rain fade duration and the prediction of the error performance and availability of digital systems.

Recommendation ITU-R R618 presents propagation data and step-by-step methods for predicting the performance of earth-space radio systems operating in frequency bands between about 1 GHz and 55 GHz and applicable to average annual percentage times in the range 0.001 per cent to 50 per cent. This recommendation deals only with effects relating to the wanted signal. Interference aspects are covered in Recommendations ITU-R P.452, P.619 and P.1412. There is insufficient space within this chapter to present all the details of the prediction methods given in Recommendation ITU-R P.618 and, therefore, a broad description will be given together with references to related ITU documents.