A wideband omnidirectional circularly polarized (CP) rectangular dielectric resonator antenna (DRA) is investigated in this communication. An inclined slot, loaded by a parasitic conducting strip, is fabricated on each sidewall of the DRA. The parasitic strips can excite a CP mode, which combines with the CP DRA mode to provide a wideband axial-ratio (AR) bandwidth of more than 25%. To fully utilize the increased AR bandwidth, the impedance bandwidth is also broadened by introducing a hollow cylinder at the center of the DRA. The hollow region is also used to accommodate a coaxial probe that excites the antenna. The reflection coefficient, AR, radiation pattern, antenna gain, and efficiency of the antenna are studied, and reasonable agreement between the measured and simulated results is observed. A parametric study was also carried out to characterize the proposed wideband CP omnidirectional antenna. © 2012 IEEE.