When electromagnetic wave propagates through the atmosphere and reaches the receiver, it takes its own path through a number of ways. Sometimes the wave arrives at the receiver after reflection from the ionosphere but ionospheric reflection is not being discussed in this book. There are certain others that may reach the receiver after reflection, the details of which will be discussed in Chapter 3. The waves may also reach the receiver after refraction and diffraction, which we will discuss in Chapter 4. The waves that arrive at the receiver after reflection from the troposphere and ionosphere are called sky waves. Waves being received by other paths, namely, space waves and surface waves, are called ground waves (Ghosh 1998). The space waves consist of waves reflected from the surface of the earth and also those received directly from the transmitter. The surface waves are guided along the earth’s surface. These electromagnetic waves propagate close to the earth’s surface and partly follow the curvature of the earth by diffraction.