English: Microwave horn antennas, used for microwave relay links to transmit telephone calls and television broadcasts between nearby cities. This type of antenna is called a Hogg or horn-reflector antenna, invented by Albert Beck and Harald Friis in 1941 and developed by D. L. Hogg at Bell Telephone laboratories, USA in 1961. It consists of a vertical flaring metal horn with a reflector mounted in its mouth at an angle of 45° so the beam is emitted horizontally (the mouth of these antennas is covered by a plastic sheet to keep out rain). The reflector is a segment of a parabolic reflector, so the antenna is equivalent to a parabolic antenna fed off-axis. Its advantage over a standard parabolic dish antenna is that it has very low sidelobes (energy radiated at angles outside of the main beam). This allows microwave relay stations to reuse the the same frequencies in several different antennas pointed in different directions, without interfering with each other.