A new singly-fed bidirectional wideband circularly polarized cylindrical dielectric resonator antenna (CDRA) using modified J-shaped ground plane is investigated and presented in this paper. The designed antenna excited by a single microstrip feed line with the modified Jshaped ground plane, which supports the orthogonal mode generation i.e. HEM11 δ mode for realizing circular polarization (CP). Measured results show that the proposed antenna achieved S11 ≤ -10 dB, input impedance bandwidth of 41.44% (centered at 3.74 GHz) and 3-dB axial ratio bandwidth in broadside direction of 29.91% (centered at 3.61 GHz). The average measured gain and simulated radiation efficiency in broadside are 2.84 dBic and 94.69% respectively, throughout the working band. The proposed CPDRA is a bidirectional radiator, and the radiation patterns on both sides are nearly the same. The antenna radiates left-handed CP wave in +z-direction and right-handed CP wave in -z-direction for both the resonance frequencies, which has been confirmed by plotting CP radiation pattern. The presented design can be used for Wi-MAX (3.3-3.7 GHz) and LTE3400 (3400-3800 MHz) bands. © 2019 RADIOENGINEERING.