The beginning of AM radio broadcasting in 1920 and the allocation of medium wave frequencies to broadcasting stations sparked an increase in interest in medium wave antennas. The flattop or T-antenna was used as the main broadcasting antenna through the 1920s. It had the disadvantage that it required two masts, twice the construction cost of a single mast antenna, far more land area, and parasitic currents in the masts distorted the radiation pattern. Two historic papers published in 1924 by Stuart Ballantine led to the development of the mast radiator. One derived the radiation resistance of a vertical monopole antenna over a ground plane. He found that the radiation resistance increased to a maximum at a length of a half wavelength, so a mast around that length had an input resistance that was much higher than the ground resistance, reducing the fraction of transmitter power that was lost in the ground system. In a second paper the same year he showed that the amount of power radiated horizontally in ground waves reached a maximum at a mast height of .625formula_15 (225 electrical degrees).