Introduction

Wireless communication systems use radio waves for exchanging information between two entities. Antenna thus becomes an important component in a wireless system because this entity can convert RF signals over a guided medium into electromagnetic waves (or radio waves). Owing to the reciprocity characteristics exhibited by all antennas, the reverse conversion also occurs in it. This enables the wireless system to transmit and receive signals using the same antenna. Figure 5.1 illustrates a block representation of a wireless communication system comprising a transmitter, feed line, Tx antenna at the sending end and Rx antenna, feed line, receiver system at the other end.

IEEE standard 145–1983 defines antenna as ‘that part of transmitting or receiving system which is designed to radiate or to receive electromagnetic wave’. They are based on the basic principle that accelerated or de-accelerated charge produces radiation.

Now-a-days, infinite varieties of antennas have been developed. Every antenna works over a narrow band of frequency for which it is designed; hence, depending upon the spectrum allotted and the requirement of each wireless system, the antenna geometry and type differs. In this chapter, the radiation principle that governs the antenna's functionality and modes of electromagnetic wave propagation will be explained before taking on topics like basic antenna parameters and families of antenna. The later part of this chapter will explain practical antenna design requirements. Finally, smart antenna and its operation principle will be explained.