A　2　x　2　circularly　polarized　(CP)　sequential　rotation　microstrip　patch　antenna　array　with　high　gain　for　long-range　ultra-high　frequency　(UHF)　radio　frequency　identification　(RFID)　communication　is　proposed　in　this　paper.　In　order　to　meet　the　operational　frequency　band　requirement　of　840-960　MHz　and,　at　the　same　time,　achieve　enhanced　broadside　gain,　a　two-level　sequential　rotation　structure　is　developed.　Series　power　divider　is　used　as　the　basic　element　of　the　feed　network　that　is　implemented　with　the　substrate-integrated　coaxial　line　technology　for　minimizing　radiation　losses.　The　manufactured　prototype　exhibits　a　peak　gain　of　12.5　dBic　at　900　MHz　and　an　axial　ratio　(AR)　bandwidth　(AR　3　dB)　of　18.2%　from　828　to　994　MHz.　In　comparison　with　the　state-of-the-art,　the　proposed　antenna　shows　an　excellent　gain/size　trade-off.