A novel electrically small, wide beamwidth circularly polarized (CP) antenna using two orthogonal smaller hybrid magnetic dipoles (HMDs) for radio frequency identification (RFID) reader application is presented, which achieves a… Click to show full abstract
A novel electrically small, wide beamwidth circularly polarized (CP) antenna using two orthogonal smaller hybrid magnetic dipoles (HMDs) for radio frequency identification (RFID) reader application is presented, which achieves a quality factor ($Q$ -factor) approaching the Chu-limit. First, a HMD is implemented by the combination of two single-slit magnetic dipoles (S-MDs) and one dual-slit magnetic dipole (D-MD), which is carefully analyzed by equivalent circuit models and field distribution. Then, by implementing two orthogonal HMDs with slightly size difference and a 45° angle tilted coupling feeding line, two orthogonal magnetic components with equal magnitude and 90° phase difference are obtained, which lead to a CP radiation. Finally, an electrically small CP magnetic dipole antenna with a size of $0.12\,\,\lambda _{0} \times 0.12\,\,\lambda _{0} \times 0.04\,\,\lambda _{0} (ka< 0.55)$ ($\lambda _{0}$ is the free-space wavelength at its center frequency) is fabricated and measured. The measurement shows that a −10 dB impedance bandwidth of 3.17% (cover 902–928 MHz UHF band well), a half power beamwidth (HPBW) of 104°, and a peak radiation gain of 4.57 dBic are achieved. Generally, it features a small size, wide beamwidth, simple design, and good radiation performance, exhibiting good application potential usage in internet of things (IoTs) systems.
