Introduction

Propagation of electromagnetic (EM) waves is basically a flow or transfer of power from the transmitter to the receiver – there is a medium in between them through which waves propagate. This is a basic consideration that any kind of propagation (like sound, heat, light, etc.) has to satisfy and is not limited to EM waves only. Two theorems are useful in this regard – Maxwell's law for time-varying electromagnetic signals, which leads the phenomenon for propagation of electromagnetic signals and Poynting's theorem, which states that the flow of power must be equal to the cross product of electric (E) field and magnetic (H) field.

P = E _H (6.1)

In this chapter, we confine our discussion mainly to the medium or space between a transmitter (Tx) and receiver (Rx) through which waves are propagated. This medium is also called the channel. The channel may be wave guided (like co-axial cables) or free space, considered as a radio link. It is not possible to describe the entire EM propagation analogy with medium characteristics within a chapter as it is very vast. As the prime focus of this book is mainly on wireless technology, we will restrict our discussion to radio medium or free space communication medium.

Radio communication operation is considered for a frequency range of 3 MHz to 300 GHz. The system includes microwave links (1–40 GHz), scatter links, satellite links and most importantly, point-to-point link or line of sight (LOS) communication mechanism.