A novel miniaturization quasi Yagi-Uda antenna based on capacitive loading technique

This paper presents a novel miniaturization quasi Yagi-Uda antenna compared with conventional antenna. The longitudinal dimension is decreased by rational layout of the feeding structure and related circuit, while its transverse dimension could be reduced by the capacitive loading technique applied on the reflector and driven dipole, which could be equivalent to extend their current flowing length. After the optimization with the software HFSS, the proposed antenna is fabricated. Its measurement results are agree with the simulation well. Its gain is around 6.8dBi, its cross polarization ratio is above 40dB at the main lobe, and the VSWR is less than 1.4 over the frequency range of American standard RFID from 902MHz to 928MHz. The size of the substrate is only 110 mm×105 mm, which is about one-third of the wavelength of center frequency in free space.