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A wideband filtering dielectric patch (DP) antenna with reconfigurable bandwidth is investigated in this paper. Adjusting the aspect ratio of the DP resonator can make the high-order TE₁₂₁ mode close to the dominate TM₁₀₁ mode to facilitate the design of wideband filtering DP antenna. Meanwhile, the high-order TM₁₁₁ mode is adjacent to the TE₁₂₁ mode and then used as a non-excitation and non-radiation mode for producing an upper band-edge radiation null. On this basis, two slots with different sizes in parallel are introduced into the ground plane to excite the DP resonator, resulting in a lower band-edge radiation null, which sharpens the lower band-edge roll off. A pair of slits between the two coupling slots are incorporated and the varactor diodes are loaded on the slits to tune the electrical distance of the coupling slots, thereby electrically controlling the frequency of the lower band-edge radiation null. In this way, the fractional bandwidth (FBW) of the resultant filtering antenna can be flexibly tuned from 21% to 15.3%. A prototype has been designed, fabricated, and measured. Reasonable agreement was obtained between the simulated and measured results.