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A compact wideband unidirectional antenna with a reflector connected to the ground using a stub is proposed in this letter. The proposed antenna consists of a pair of stepped-structure patches and a coplanar waveguide feeding line. One stepped-structure patch is used as a monopole radiator, while the other operates as a reflector. As discussed, when the connection area between the reflector and the ground is small, the antenna can provide unidirectional radiation patterns over the operating frequency band ranging from 3.82 to 5.63 GHz for return loss greater than 10 dB. In this investigation, the optimized size of the proposed antenna is 20 × 20 mm2, which is much smaller than most of the current wideband unidirectional antennas. Experimental and simulated results are shown and discussed for practical applications.