The great majority of AM broadcsters utilize 1/4 wave vertical radiators, with a pi-network ATU to present a +/- 0j load to the transmission line. This radiator can be a simple steel tower, or in some cases a folded monopole, with 3 or more skirt wires suspended about 1 meter away from the tower, and bonded together at the base and top of the support structure.
The "Funipole" , fed from the bottom of the skirt, has the advantages of using a grounded tower, making it simple to attach FM, studio-to-transmitter, and communications antennas to the structure without isocouplers presenting detuning problems, and are inherently broadbanded. Though NRSC and FCC rules have restricted AM audio bandwith, audio quality used to be a major selling point for these antennas.
73 DE,
Ted K4TML