a mm - wave antenna apparatus with beam steering function that includes : a butler matrix feeding network ; a plurality of power combiners , each power combiner having one input and n outputs , configured to apply equal phase and power to a phase distributed output signal generated by the butler matrix feeding network and to generate n processed signals ; and a plurality of millimeter wave switched beam planar antenna arrays having at least 1 . 5 ghz of bandwidth and located on a top low loss dielectric substrate , each antenna array of n elements , configured to obtain direct and narrow width beams from the n processed signals combined by each power combiner .