When a radio-frequency current flows into a transmitting antenna power is radiated in a number of directions in what is called an electromagnetic wave. These waves travel at the same speed as light and can be reflected and refracted just as light can be. Some antennas are designed to be highly directional, some are omnidirectional. The radiated energy will reach the receiving station by one or more of five different modes as shown in Fig. 37.7.
Fig. 37.7 Modes of propagation of radio waves