A high-gain and broadband printed Yagi-Uda antenna is proposed. The microstripline-to-balance microstripline technique is adopted in the feeding mode of the active dipole, which can help to realize the balanced-unbalanced transformation. The ground of the microstrip feeding line can function as a reflector, and both the longer reflector and the shorter director can also help the antenna achieve wideband. By altering the area of the substrate, the antenna gain can be effectively improved. A printed Yagi-Uda antenna operating at 3.5 GHz has been designed and manufactured. Both the simulated and measured results indicate that there is a high positive correlation between antenna gain and the substrate area extended from the front of the director, and antenna broadband characteristic would not be changed at the same time. Moreover, the impedance bandwidth of the proposed antenna can achieve 27.4%, and the maximum gain in the operating band can reach 10.6 dBi.
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