TABLE OF CONTENTS The nature of radio signals and the way in which they travel are a key elements in cellular systems. The frequencies that are used are chosen as a result of many factors, some of which are technical and others resulting from spectrum allocation issues. Nevertheless, technical issues play a key role in determining many features associated with the cellular networks and are thus of great importance. The nature of the signals, the way they travel and how they are influenced by their surroundings play a major part in determining how a network is planned.
Radio waves are a form of radiation known as electromagnetic waves. As they contain both electric and magnetic elements, it is necessary to take a look at these fields before looking at the electromagnetic wave itself.
Any electrically charged object, whether it has a static charge or is carrying a current, has an electric field associated with it. It is a commonly known fact that like charges repel one another and opposite charges attract. This can be demonstrated in a number of ways. For example, hair often tends to stand up after it has been brushed or combed. The brushing action generates an electrostatic charge on the hairs and, as they all have the same type of charge, they tend to repel one another and stand up. In this way it can be seen that a force is exerted between them. Examples like this are quite dramatic, and result because the voltages that are...
