4-4
Figure 4-3.—Typical antennas.
CURRENT AND VOLTAGE DISTRIBUTION ON AN ANTENNA
A current flowing in a wire whose length is properly related to the rf produces an electro magnetic
field. This field is radiated from the wire and is set free in space. We will discuss how these waves are set
free later in this chapter. Remember, the principles of radiation of electromagnetic energy are based on
two laws:
1. A MOVING ELECTRIC FIELD CREATES A MAGNETIC (H) FIELD.
2. A MOVING MAGNETIC FIELD CREATES AN ELECTRIC (E) FIELD.
In space, these two fields will be in phase and perpendicular to each other at any given time.
Although a conductor is usually considered present when a moving electric or magnetic field is
mentioned, the laws that govern these fields say nothing about a conductor. Therefore, these laws hold
true whether a conductor is present or not.
