Electromagnetic waves having frequency greater than that of the television signals are known as Microwaves. These waves have very less wavelength nearly few millimeters. Due to their low wavelength, these waves bend properly from the corners of the objects coming in their way. These are basically used to generate beam signals in fixed directions. By using the microwaves in the radars these can be used to detect the flying objects. So, it is clear that these waves can detect the flying objects. If these have the ability to detect the flying objects then these can also measure the speed of the flying objects. Microwaves basically travel with the speed of light.
If we want to use these microwaves on earth’s surface then the sending and receiving antennas must be able to see each other. All the antennas which are used between the sending and receiving antennas are known as repeaters. The function of repeater is to increase the intensity of the weak signal. Repeaters amplify the signal again and pass it to the next repeater installed. The cost of installing repeaters is too much. This method can’t be used to cover the whole surface of earth. Other reason is that the earth has lots of oceans on its surface. So, implementation is not possible. To remove this limitation communication satellites were used. America launched the first communication satellite in the year 1958.
