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A frequency switchable printed Yagi-Uda dipole sub-array is proposed as an array element for base station antennas. The sub-array consists of four Yagi-Uda dipole elements loaded with PIN diodes. The electrical lengths of the director and driven dipole elements can be changed by controlling the PIN diodes states so that the sub-array can operate in two different frequency bands. The impedance bandwidth (|S11|≤ -10dB) is measured to be 4.9% and 12.9% in the lower (from 2.39 to 2.51 GHz) and higher band (from 3.18 to 3.62 GHz), respectively. The measured gain of the sub-array is 9.2 and 11.9 dBi at 2.44 and 3.4 GHz, respectively. The end-fire fan-beam pattern is obtained across the two operation bands, which makes the antenna element suitable for base station application with frequency reconfigurablity.