Page 28 - Antennas for Base Stations in Wireless Communications

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Chapter

Fundamentals of Antennas

Ahmed A. Kishk
Center of Electromagnetic System Research (CEDAR)
Department of Electrical Engineering
University of Mississippi

An antenna is a device that is used to transfer guided electromagnetic
waves (signals) to radiating waves in an unbounded medium, usually
free space, and vice versa (i.e., in either the transmitting or receiving
mode of operation). Antennas are frequency-dependent devices. Each
antenna is designed for a certain frequency band. Beyond the operating
band, the antenna rejects the signal. Therefore, we might look at the
antenna as a bandpass filter and a transducer. Antennas are essential
parts in communication systems. Therefore, understanding their prin-
ciples is important. In this chapter, we introduce the reader to antenna
fundamentals.
There are many different antenna types. The isotropic point source
radiator, one of the basic theoretical radiators, is useful because it can
be considered a reference to other antennas. The isotropic point source
radiator radiates equally in all directions in free space. Physically, such
an isotropic point source cannot exist. Most antennas’ gains are mea-
sured with reference to an isotropic radiator and are rated in decibels
with respect to an isotropic radiator (dBi).

1.1 Basis Parameters and
Definitions of Antennas

Some basic parameters affect an antenna’s performance. The designer
must consider these design parameters and should be able to adjust,
as needed, during the design process the frequency band of operation,

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