A　planar　switchable　phased　array　has　been　proposed　for　5G　handset　terminals　at　28GHz.　It　consists　of　three　subarrays.　Each　subarray　contains　eight　radiating　slots.　The　three　subarrays　share　the　same　ground　plane　and　can　steer　their　beams　to　three　distinct　regions.　By　switching　between　the　three　subarrays,　a　three-dimensional　(3-D)　coverage　of　the　terminal　is　obtained.　However,　the　array　suffers　from　relatively　high　mutual　coupling.　Hence,　in　this　work,　an　effective　decoupling　technique　is　proposed　to　reduce　the　mutual　coupling　between　adjacent　elements　of　each　subarray,　while　preserving　the　matching　conditions　and　radiation　characteristics　of　the　original　handset　array.　The　isolation　within　each　array　is　enhanced　more　than　5dB,　achieving　an　isolation　larger　than　18dB　at　the　center　frequency,　resulting　in　smaller　active　reflection　and　larger　scanning　angle.　©　2019　IEEE.