equency radio signal. The OU contains radio frequency transmitters and receivers. Due this feature, it is also known as a radio transceiver. When the signal is received from the antenna, it usually passes the low noise amplifier (LNA), which strengthens the weak signals. This is followed by automatic gain control (AGE), which ensures equality of the signal strength when entering the radio receiver. The difference between the LNA and AGC is that while the former is used for received signal clarity and quality maintenance of the received signal, the latter compensates the signal power attenuated during transmission due to unpredictable climatic conditions. This signal is then demodulated into an intermediate frequency (IF) or a base band (BB) signal before it moves to the IU. The OU gets electrical power and the low frequency modulated signal from the IU through coaxial cable connections. Antenna An antenna is the unit of the microwave link that interacts with free space; hence its understanding becomes critical for the microwave link planning engineers. An antenna is defined as the structure that transfers the electromagnetic energy from the free space into transmission lines and vice versa. There are many types of antennas: horn, parabolic, flat or planar, lens, yagi, array, etc. The application of the Transmission Network Planning and Optimisation antenna depends upon its electrical and mechanical characteristics. Some of the important characteristics of an antenna are now given. Antenna Directivity The directivity D(0, 0) is defined as the ratio of the radiation intensity P(0, ), which is the power radiated per unit solid angle in the direction (A, ), to the average radiation intensity (the average power radiated from an antenna per unit solid angle): (3.1) where Pt = total radiated power O = elevation angle = azimuth angle Pav = average radiation intensity Antenna Gain The power gain G(0, 0) of an antenna in the direction (A, ) is defined by (3.2) where P(O, ) = radiation intensity Pi = total power supplied to