Because the radio wave travel in narrow beams confined to a line – of – sight path from one antenna to the other, they don’t interfere with other microwave equipment, and nearby microwave links can use the same frequencies. Antenna used must be highly directional (High gain); these antenna are installed in elevated location such as large radio towers in order to be able to transmit across long distances. Typical types of antenna used in radio relay links installations are parabolic antenna, dielectric lens, and horn – reflector antenna, which have a diameter of up to be 4 meters. Highly directive antennas permit an economical use of the available frequency spectrum, despite long transmission distances.