A Novel Design of Folded Dipole for Broadband Printed Yagi-Uda Antenna

In this paper, a printed wideband Yagi-Uda antenna with a novel folded dipole driver is proposed. The folded dipole driver is comprised of a folded dipole and a microstrip feedline which functions as an internal balun to mainly determine its wide impedance bandwidth. With the optimized parameters, an operating band of 1.69 GHz ∼ 2.72 GHz can be obtained. Besides the folded dipole driver, the broadband printed Yagi-Uda antenna also consists of three directors and a reflector. Its wideband performance is mainly determined by the folded dipole driver, while the reflector and directors improve its performance slightly. By optimizing the geometrical parameters of the folded dipole driver, a bandwidth of 61.8% (1.53GHz ∼ 2.93GHz) for return loss being higher than 10 dB is achieved. The proposed printed Yagi-Uda antenna is realized on FR4 substrate with a measured operating bandwidth of 62% (1.51GHz ∼ 2.94GHz), a flat gain (5.6 dB ∼ 7.3 dB), more than 10 dB front-to-back ratio and lower than −15 dB cross-polarization level.