Recently, a few UHF CP tag antennas have been
proposed in literature [2-4]. In [2], a coupling-feed circularly
polarized tag antenna has been proposed. The antenna has a
size of 00 0 0.23 0.23 0.005 λλ λ × × at 925 MHz and a 3-dB
AR bandwidth of 6 MHz. A square-shaped microstrip RFID
tag antenna has also been proposed for CP radiation [3]. It
has exhibited a surface area of 00 0 0.33 0.33 0.005 λλ λ × × at
915MHz and a 3-dB AR bandwidth of 20 MHz. A circular
microstrip RFID tag antenna for CP radiation has been
proposed in [4]. The antenna has a size of
00 0 0.24 0.24 0.005 λλ λ × × at 915 MHz and a 3-dB AR
bandwidth of 6 MHz. There is no doubt that these designs
are good jobs, but their 3-dB AR bandwidths cannot cover
the RFID bands of North and South America (902–928 MHz,
FCC band). In this paper, the proposed antenna exhibits a
surface area of 00 0 0.21 0.21 0.003 λλ λ × × at 915 MHz. And
the antenna has a much wider 3-dB AR bandwidth of
31MHz (903-934 MHz) that covers the RFID bands of North
and South America and Taiwan (920–928 MHz).