A patch antenna system operating in the 2.4-2.5 GHz ISM band is proposed for in-band full duplex applications. The proposed antenna consists of a patch antenna, a modified 180˚ hybrid, and a defected ground structure. Fabricated prototype results show a measured bandwidth of 100 MHz and an isolation of -75 dB at the center frequency with an isolation of at least -50 dB covering the ISM band 2.4 GHz-2.5 GHz. The design also has a spherical directional radiation pattern, low cross polarization, and reasonable gain values.
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