In this communication, we introduce a p-i-n-diode-based polarizer integrated with a dielectric resonator antenna (DRA) to realize a polarization reconfigurability. The p-i-n-diode-based polarizer is found to be effective in altering the electromagnetic-field distribution of the DRA, such that the polarization of the DRA can be actively changed. Unlike conventional p-i-n-diode-based reconfigurable antennas, the proposed active polarizer would not degrade radiation performance of the DRA. In this way, the antenna retains the high radiation efficiency with its simple excitation. The proposed antenna uses a simple and agile-switching mechanism to provide three switchable polarizations to the DRA including: a y -axis polarization (STATE 1), a +45° polarization (STATE 2), and a -45° polarization (STATE 3) across a wide effective bandwidth (overlapped bands of three states) of 15.0%. The radiation efficiencies maintain 65%-79% in each state throughout the effective operating band. Finally, the experimental results agree well with the theoretical analyses.