The previous generations of cellular networks are almost packed in the UHF band with a frequency range of 300 MHz - 3 GHz in the radio spectrum. Recently, the Ka-band is under investigation to be commercially used in next generation of cellular systems, due to the spectrum availability and the small size of the components. The main purpose of this paper is to design a wideband antenna element at 28 GHz, so that it can be used in the antenna arrays of next generation mobile networks. The proposed unit-cell is a proximity coupled stacked patch antenna. The antenna parameters and characteristics are investigated both through simulation and measurement. The antenna achieves a measured gain of 7.1 dB at 28 GHz. The measured impedance bandwidth and 1-dB gain bandwidth are 34.48 % and 17.4 %, respectively.