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Abstract-In this paper, a dual-fed circularly polarized antenna design with high isolation is presented for radio frequency identification (RFID) reader. The proposed antenna is excited by two fed ports connected with a circular split-ring microstrip line underneath the ground plane. A radial aperture in the ground plane provides coupling between the split-ring microstrip and radiating patch. For multiple RFID band requirements, the dimension of the aperture can be modified to obtain high isolation on different RFID Band. Finally, an antenna prototype for China RFID Band (920-925 MHz) is fabricated. The measured results agree well with simulation, and show 10-dB matching bandwidth of 18% (820-1000 MHz), 3-dB axial ratio (AR) bandwidth of 11% (854-960 MHz), and 25-dB isolation bandwidth of 11 MHz (917-928 MHz).

A novel type of radio frequency identification (RFID) reader antenna is proposed for mobile ultra-high frequency (UHF) RFID device. By folded-dipole loop structure with parasitic element, a small antenna size of 31 * 31 * 1.6 mm 3 is achieved. The antenna with different parasitic element size can work on different UHF RFID bands. The antenna prototype is fabricated and the measured bandwidth is around 13.5 MHz (915.5-929 MHz), which covers the China RFID Band (920-925 MHz). The measured reading distance achieves 65 mm with the near-field RFID tag and 1.17 m with the far-field tag. The measurement agrees well with simulated result and shows that antenna is desirable for both near-field and far-field UHF RFID applications.

Abstract-In this paper, a novel technique for planar inverted-F antenna (PIFA) with broadband circular polarization and pattern diversity is proposed. A defeated ground structure (DGS) has achieved broadband circular polarized (CP) PIFA by using a square branch at the ground corner with arrow-shaped slot. The pattern diversity PIFA system consists of two CP PIFAs placed symmetrically on the diagonal of DGS. Furthermore, the DGS improves port-to-port isolation by using another smaller square branch at the opposite ground corner. Finally, a prototype is fabricated and measured. The measured results agree well with simulation, and show 10-dB matching bandwidth of 16.3% (825-986 MHz), 3-dB axial ratio (AR) bandwidth of 15.5% (830-982 MHz), and 25-dB isolation bandwidth of 12.4% (848-968 MHz), which shows suitability for radio-frequencyidentification (RFID) application.

A compact loop antenna is presented for mobile ultrahigh frequency (UHF) radio frequency identification (RFID) application. This antenna, printed on a 0.8 mm thick FR4 substrate with a small size of 31 mm × 31 mm, achieves good impedance bandwidth from 897 to 928 MHz, which covers USA RFID Band (902–928 MHz). The proposed loop configuration, with a split-ring resonator (SRR) coupled inside it, demonstrates strong and uniform magnetic field distribution in the near-field antenna region. Its linearly polarized radiation pattern provides available far-field gain. Finally, the reading capabilities of antenna are up to 56 mm for near-field and 1.05 m for far-field UHF RFID operations, respectively.