In order to realize practically applicable beam forming antennas, this paper has analyzed gain variation (which is the disadvantage of beam forming antennas with discrete phase shifters) of 4- and 8- element beam forming antennas with discrete (90 degree) phase shifters. The heuristic computer simulations have shown the gain variation is less than 1 dB for both 4- and 8- element antennas and beam forming antennas with discrete (90 degree) phase shifters with an appropriate set of phases for each antenna element is practically applicable. Further, four-element slot type antennas have been fabricated for performance validation. The measured results show a 10 dBi antenna gain with a less than 1 dB gain variation and 66 degree antenna steering capability. Thus, this paper has proved the beam forming antenna with discrete (90 degree step) phase shifters is practically applicable for portable terminals in Super Broad Band Wireless Communications Systems and so on.