Circularly polarized beam-steering antenna array for ultra-high frequency radio frequency identification applications

A circularly polarized beam-steering antenna array with Butler matrix is designed in this letter for ultra-high frequency radio frequency identification applications. To achieve the identification of the fast-moving tag groups, a 3 x 4 Butler matrix is utilized to switch the radiation directions at -25 degrees, 0 degrees, and +25 degrees, respectively. Besides, series-fed patch antenna element is designed and the 1 x 4 antenna array is built with element rotation for a good polarization performance. Finally, the proposed antenna system is fabricated and the identification area and radiation performance are tested.