ANTENNA FUNDAMENTALS

In this chapter, the basic concept of an antenna is provided and its working is explained.
Next, some critical performance parameters of antennas are discussed. Finally, some common
types of antennas are introduced.

2.1 Introduction
Antennas are metallic structures designed for radiating and receiving electromagnetic
energy. An antenna acts as a transitional structure between the guiding device (e.g. waveguide,
transmission line) and the free space. The official IEEE definition of an antenna as given by
Stutzman and Thiele [4] follows the concept: “That part of a transmitting or receiving system
that is designed to radiate or receive electromagnetic waves”.

2.2 How an Antenna radiates
In order to know how an antenna radiates, let us first consider how radiation occurs. A
conducting wire radiates mainly because of time-varying current or an acceleration (or
deceleration) of charge. If there is no motion of charges in a wire, no radiation takes place, since
no flow of current occurs. Radiation will not occur even if charges are moving with uniform
velocity along a straight wire. However, charges moving with uniform velocity along a curved or
bent wire will produce radiation. If the charge is oscillating with time, then radiation occurs even
along a straight wire as explained by Balanis [5].