An antenna for a wireless sensor network for an indoor environment is proposed. The proposed antenna is composed of an artificial magnetic conductor reflector, two branched radiators, and a power divider including a switched-line phase shifter. Two branched radiators act as four bent monopoles or two crossed dipoles by the switched-line phase shifter. The power divider provides two branched radiators inphase or out of phase power which makes a side directional pattern or a normal directional pattern, respectively. The proposed antenna has less than 10 mm height with 100 × 100 mm area and more than 100 MHz bandwidth at 2.4 GHz.