If you had been around in the early days of electronics, you would have
considered an antenna (aerial) to be little more than a piece of wire strung
between two trees or upright poles. In those days, technicians assumed
that longer antennas automatically provided better reception than shorter
antennas. They also believed that a mysterious medium filled all space,
and that an antenna used this medium to send and receive its energy.
These two assumptions have since been discarded. Modern antennas have
evolved to the point that highly directional, specially designed antennas
satellites and Earth station antennas (figure 4-1). Present transmission
theories are based on the assumption that space itself is the only medium
necessary to propagate (transmit) radio energy.
4-1. A tremendous amount of knowledge and information has been gained
about the design of antennas and radio wave propagation. Still, many old-time
technicians will tell you that when it comes to designing the length of an
antenna, the best procedure is to perform all calculations and try out the
antenna. If it doesn't work right, use a cut-and-try method until it does.
Fortunately, enough information has been collected over the last few decades
that it is now possible to predict the behavior of antennas. This chapter discusses
and explains the basic design and operation of antennas.