An Electrically Small Antenna with a Bidirectional Radiation Pattern for UHF RFID Tags

In this paper, an electrically small antenna with a bidirectional radiation pattern for ultra high frequency (UHF) radio frequency identification (RFID) tags is proposed. The antenna, whose size is less than 0.04λ
₀
×0.04λ
₀
( λ
₀
is the corresponding wavelength of the operating frequency at 915 MHz), is comprised of a folded loop and a split ring resonator (SRR) structure. Simulated results show that the impedance bandwidth of the proposed antenna can cover the operating frequency of worldwide UHF RFID applications, from 840 MHz to 960 MHz, and at the same time a bidirectional radiation pattern is obtained. Moreover, when proposed antennas are stacked or tiled together, there are no obvious effects on their resonant frequency and gain pattern.