Modified two-element Yagi-uda antenna with tunable beams

A modified two-element Yagi-Uda antenna with tunable beams in the H-plane (including four significant beams: forward, backward, omni-directional, and bi-directional beams) is presented. These tunable beams are achieved by simply adjusting the short-circuit position of the transmission line connected to the parasitic element. The principle of operation is investigated by examining the current relations between the driven and parasitic elements. Measured results of a fabricated prototype are presented and discussed.