A differentially fed dual-polarized patch antenna with wide bandwidth is presented in this paper using Substrate-Integrated Waveguide (SIW) technology. The antenna comprises a circular patch radiator, a square SIW cavity and four symmetric arc-shaped slots. The circular patch is internally embedded in the square SIW cavity with a surrounded ring slot. Two pairs of differential L-shaped probes are used for the excitation of the differential signals. These signals excite the orthogonal linearly-polarized modes. The dominant resonant mode of the circular patch resonator (TM11) and the modes of the SIW cavity (TE110 and TE120/TE210) are employed to achieve effective radiation under these resonances. Besides, four symmetric arc-shaped slots are etched on the top surface of the cavity to enhance the impedance bandwidth. The resonant properties of these modes are studied based on the cavity model theory. Then, their resonant frequencies are discussed to provide information for designing and optimizing such an antenna. Finally, the feeding positions of the differential L-shaped probes are investigated for good impedance matching. The proposed antenna has been fabricated and measured. The measured results show that the proposed antenna achieves a wide impedance bandwidth of about 64.8% (4.37-8.56 GHz) and 64.2% (4.48-8.72 GHz) for horizontal and vertical polarization, respectively. High differential isolation of better than 30 dB and low cross-polarization are obtained by adopting the differential feeding mechanism. Due to the SIW cavity-backed structure, the antenna shows unidirectional radiation patterns and low back-lobe radiation, making it conveniently integrated with microwave differential circuits and applied in the base station systems.
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