A dual linearly-polarized antenna subarray that operates at 28 GHz and 38 GHz is proposed for fifth generation (5G) base stations. In contrast to earlier millimeter-wave base-station antennas that implement individual single-band antennas, simultaneous realization of dual-band operation can save space and cost. In addition, the proposed subarray depicts dual polarizations, improving signal reliability through polarization diversity. Furthermore, the proposed subarray is scalable and expandable in size and aperture. The proposed antenna subarray consists of 2 × 2 dual off-center-fed dipoles. The dual-band feature is obtained by tailoring the structure for expanding current pathways and impedance bandwidths. Accordingly, the impedance bandwidths for the lower and higher bands are 27.2-30.2 GHz and 35.7-40.3 GHz, respectively. When uniformly-distributed currents are excited, the proposed antenna shows broadside radiation with peak gain of 13.1 dBi at 28 GHz and 13.2 dBi at 38 GHz. When various current phases are excited, the subarray provides a scanning range of ±18°. The scalability is demonstrated by an example large-scale array that comprises 4 × 4 elements. The S-parameters are robust, and the gain is enhanced as 19.6 dBi at 28 GHz and 17.8 dBi at 38 GHz. Meanwhile, a broader scanning range of ±45° can be obtained. INDEX TERMS 5G mobile communication, antenna arrays, base stations, multifrequency antennas.