Three antennas broadcast in phase at a wavelength of 1 km. The antennas arc separated by a...

Three antennas broadcast in phase at a wavelength of 1 km. The antennas arc separated by a distance of km and each antenna radiates equally in all horizontal directions. Because of interference, a broadcast “beam” is limited by interference minima. How many well-defined beams are broadcast and what are their angular half-widths?