The folded unipole antenna is a type of monopole mast radiator antenna used as a transmitting antenna mainly in the medium wave band for AM radio broadcasting stations. It consists of a vertical metal rod or mast mounted over and connected at its base to a grounding system consisting of buried wires. The mast is surrounded by a "skirt" of vertical wires electrically attached at or near the top of the mast. The skirt wires are connected by a metal ring near the mast base, and the feedline feeding power from the transmitter is connected between the ring and the ground.
It has seen much use for refurbishing medium wave AM broadcasting station towers in the United States and other countries. When an AM radio station shares a tower with other antennas such as FM broadcasting antennas, the folded unipole is often a good choice. Since the base of the tower connects to the ground system, unlike in an ordinary mast radiator tower in which the base is at high voltage, the transmission lines to any antennas mounted on the tower, as well as aircraft lighting power lines, can be run up the side of the tower without requiring isolators.[1]