This paper presents a 28-GHz slotted substrate integrated waveguide (SIW) antenna with end-fire radiation pattern for future 5G mobile handset. A pair of transverse slots is used in the broad faces to suppress back lobe radiation. The simulated 10-dB return loss bandwidth of the proposed SIW antenna is 26.9 GHz to 29.8 GHz. The proposed antenna achieves HPBW of 144.9° and gain of 5 dB with 98.8 % radiation efficiency. In comparison with open ended SIW front to back radiation ratio is increased up to 40 dB in this antenna. In order to achieve full spherical coverage, two beam steerable 4×1 subarrays could be employed in the top and bottom edges of the handset. The compactness, low cost and good performance of the proposed antenna make it an appropriate choice for the future 5G mobile handset.