PLANAR, LIGHTWEIGHT, CIRCULARLY POLARIZED CROSSED DIPOLE ANTENNA FOR HANDHELD UHF RFID READER

摘要

A planar, lightweight, crossed dipole antenna with circularly polarized (CP) radiation is introduced for application in a radiofrequency identification handheld reader at ultrahigh frequency bands. The dipoles cross through a 90° phase-delay line of a vacant-quarter printed ring that enables broadband characteristic in terms of impedance matching and 3-dB axial ratio (AR) bandwidths. Four printed inductors are symmetrically inserted into the dipole arms whose ends are barbed to achieve a compact size. A sample antenna with a size of 60×60×0.508 mm and weight of 3.6 g is designed, fabricated, and measured. The proposed antenna yields an impedance bandwidth of 851-941 MHz for |S_(11)|<-10 dB and a 3-dB AR bandwidth of 902-921 MHz. At 910 MHz, the antenna radiates bidirectional CP waves with a gain of 1.4 dBic and an AR of 1.1 dB.