In this letter, a three-port omnidirectional cylindrical dielectric resonator antenna (DRA) is presented. The design makes use of the TM 01 δ and two degenerate HEM 21 δ modes of the cylindrical DRA. The resonant features of the two modes are investigated and their resonant frequencies are different. The TM 01 δ mode is fed with horizontal magnetic current, which is obtained by four slots. The input impedance of the antenna is affected by the length of the open-circuit stub, which is the end of the feed network. Thus, the resonant frequency of the TM 01 δ mode can be moved to that of the HEM 21 δ one through the proposed exciting method. Two HEM 21 δ modes are excited simultaneously by a 90° hybrid coupler to realize right- and left-hand circularly polarized omnidirectional radiation. Based on the three modes, a three-port three-polarization DRA with omnidirectional radiation for indoor communication applications is fabricated and measured. The results indicate that the S -parameters, field characteristics, and communication performance are satisfactory in the operating band.