Minimizing the size of mobile antennas is necessary for integrating the components inside a mobile device. Wideband and multiband antennas are also required to cover various 5G mobile communication frequency spectra. This article presents a vertically stacked dipole antenna array operating in the 28/38 GHz dual-band. The proposed antenna is small and satisfies the need for wide bandwidth in the form of a dual band. The antenna structure has symmetric 38 GHz band radiators positioned above and below a multilayer substrate, and a 28 GHz band radiator positioned on the middle plane, providing a dual-band antenna structure with small lateral width. Herein, two types of antenna structures are proposed, each with a single-ended and differential feed structure for compatibility with various RF front ends. The single antenna yields -10 dB bandwidth for return loss of 23.9% and 14.4%, and gain of 4.8 and 4.6 dBi at 28 and 38.5 GHz, respectively. The 4-element antenna array yields a gain of 9.0 dBi at 28 GHz and 10.3 dBi at 38.5 GHz. It was fabricated on a flexible substrate and can be bent and inserted into the lateral edge of the terminal. The proposed antenna elements and arrays satisfy the performance factors requisite for millimeter wave 5G communication including compact size, wideband, dual-band, and adequate gain.