Common Radio Aerial and signal theory that exists across the radio spectrum. The following information prevails for whether it's CB radio, police radio, Television, broadcast radio, marine radio, airline radio, mobile phones etc. A signal raidates from an aerial in a certain pattern.
Different aerials radiate signals in different patterns.
For instance, a single standard vertical aerial will send out signals 360 degrees all around but not really up or down. A signal will hit the Atmoshpere from the radiation angle, which is simply the angle at which the waves are travelling. From the top tip and bottom tip of an aerial is the least signal coming out, like the light from a flourescent bulb. When this same aerial is sitting horizontally, all though the pattern doesn't change that much the waves are now up and down, instead of all around. The tips of this aerial will again transmit the least.