Electromagnetic waves do not travel in a straight line. Instead, they travel by expanding
in all directions away from the antenna. To get a visual image, think of dropping a pebble
into a pond when the surface is still. Where it drops in, the pebble sets the water’s
surface into a cyclic motion. The waves that result begin small and expand outward, only
to be replaced by new waves. In free space, the electromagnetic waves expand outward
in all three dimensions.
Figure 1-4 shows a simple idealistic antenna that is a single point at the end of a wire.
The waves produced expand outward in a spherical shape. The waves will eventually
reach the receiver, in addition to many other locations in other directions.