Indoor Wireless Communications

6Antennas

So far, we have discussed the way radio waves propagate through various media and how the specific constitutive parameters of materials have an effect on this propagation. Propagation effects such as reflection, refraction, scattering and diffraction are present in many practical situations, hence making the task of estimating the received signal strength in a wireless link a challenge. Furthermore, we have defined the concept of path loss and described various propagation models that aim at predicting this path loss more accurately, so that system designers can make use of these tools in designing efficient radio systems. When the link budget concept was examined, we mentioned that we needed ‘antennas’ at transmitter and receiver ends in order to send signals wirelessly, but did not attempt to go any further in our analysis – we simply assumed that antennas produce a gain while transmitting or receiving that should be accounted for. It is time now to discuss in detail what antennas are, to gain a better understanding and to be able to select such devices for specific applications for indoor wireless projects. Note that the aim of this chapter is not to provide a thorough analysis of antennas and electromagnetic effects, as in Hayt and Buck (2005), Kraus and Fleisch (1999) and Sadiku (2007), but rather to understand their basic characteristics, specifications and performance parameters needed to select the right antennas for given indoor requirements.

6.1 The Basics ...