In this letter, a novel series-fed periodic microstrip antenna array with reduced beam squint is proposed for the 28 GHz mm-wave 5G band. To mitigate beam squint, the design reduces the dispersion in the unit cell by introducing an L-shaped slot pair on an elliptical microstrip patch. Further improvements are achieved by utilization of the corresponding tapering and matching sections. The proposed array has a low beam squint angle of only 2◦ over a 3 GHz bandwidth, which is a decade lower than the conventional series-fed microstrip rectangular patch array. The gain fluctuation is limited to ±1.5 dB between 26.5 GHz and 29.5 GHz. Moreover, the final antenna achieves an angular coverage from −37◦ to 40◦. With its beam squint assessment capability, the proposed multibeam solution is a promising candidate for mm-Wave 5G cellular applications.