Design of Printed Yagi Antenna with Additional Driven Element for WLAN Applications

A new configuration of Yagi antenna is proposed, which can improve the forward/backward ratio (f/b) significantly while maintaining a high gain. This configuration involves the addition of one radiating element (dipole) to the original Yagi array which produces a controllable pattern used for cancellation of back lobe. This additional element may arrange on parallel (side-by-side) or collinear to a radiating dipole of the original Yagi antenna. It is shown here that the technique is most effective for collinear configuration (exhibits smaller mutual effects) and that there then exists an optimum length and position for the added element. The amplitude of the excitation of the additional element determines the angular location of the back lobe reduction. To demonstrate the major benefits, comparisons are made among the proposed and conventional Yagi configurations. Numerical and measured results of our design show more than 20 dB front to back ratio at 2.4 GHz. To the author's knowledge, this is the first printed Yagi antenna presented that has a high gain and a high f/b ratio designed using simple technique. Moreover, the proposed array represents a simple and valuable alternative to the stack Yagi antennas as the obtainable radiation characteristics are satisfactory in terms of both forward and backward gain.