A dual-wideband circularly polarized (CP) antenna was proposed based on the strategy of combining multi-mode resonances. The primary radiators were two barbed-shape dipoles and two bowtie dipoles printed on the same substrate. They were placed over an artificial magnetic conductor (AMC) for the low-profile antenna design purpose. Properly combining the fundamental mode of the barbed-shape dipole, the bowtie mode, the slot mode, the second mode of a barbed-shape dipole and extra resonance generated by the AMC surface, a dual-wideband operation can be achieved. The final design with an overall size of 0.64 λ o × 0.64 λ o × 0.16 λ o at 2.4 GHz had measured impedance bandwidth of 40% (2-3 GHz) and 49.5% (3.8-6.3 GHz) for the lower and upper bands, respectively. The measured 3 dB axial ratio bandwidths were 19.3% (2.25-2.73 GHz) and 33.8% (4.3-6.05 GHz) for the lower and upper bands, respectively. The antenna performed an average gain of about 6.6 dBic across the low CP region and 7.4 dBic across the high CP region.Index Terms-circular polarization, dual band, broadband, artificial magnetic conductor, crossed dipole 1536-1225 (c)
A compact circularly polarized (CP) crossed-dipole antenna for radio frequency identification in the ultra-high frequency is proposed. The antenna consists of two orthogonal dipoles with an arm comprised of a meander line and triangular-shaped ending for achieving a compact size. A modified T-match with a meander line is used for impedance matching between the antenna and the tag chip. In this design, CP excitation is achieved by incorporating two semi-circular curves inserted between the orthogonally arranged dipole arms. The final design, with the dimensions of 35.6 × 35.6 × 0.508 mm 3 , yields a -10-dB impedance bandwidth of 37 MHz (892-929 MHz) and a 3-dB axial ratio bandwidth of 11.4 MHz (905.2-916.6 MHz). The measured results show that the proposed tag antenna can provide a maximum reading distance of approximately 7.6 m with an effective isotropic radiated power of 3.28 W over the CP operational bandwidth.Index Terms-circular polarization, crossed dipole, meander line, radio frequency identification, tag antenna
I. INTRODUCTIONN recent years, radio frequency identification technology (RFID) in the ultra-high frequency (UHF; 860-940 MHz) band becomes mainstream applications that help the speed of handling manufactured goods and materials [1]. RFID systems are composed of at least three core components: RFID tags, RFID readers, and databases that associate arbitrary records with tag identifying data. It is obvious that a tag antenna plays a key role in overall RFID system performance factors because passive tags obtain energy from the incoming radio frequency communication signal. Therefore, the tag antenna has substantial effects on the reading distance, the overall size, and the compatibility with the tagged object of RFID systems. To date, many miniaturized tag antennas, such as a planar meander-line antenna [2], loop-fed antenna [3], modified folded dipole antenna [4,5], monopole with helical strips and vias [6], and printed symmetric inverted-F antenna with a quasi-isotropic radiation pattern [7]-[9], have been proposed for the RFID system. However, all the above-presented miniaturized tag 1536-1225 (c)
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