A High-Isolation Monopole Array With Ring Hybrid Feeding Structure for In-Band Full-Duplex Systems

A compact antenna system operating in the 2.4-GHz WLAN band is presented for in-band full-duplex operation. The design includes two monopoles over a T-shaped defected ground structure fed by a 180° hybrid. The measured -10-dB bandwidths are 9% (220 MHz) and 5% (130 MHz) for the transmitting and receiving ports, respectively. Through the entire band of interest, the antenna has a measured isolation (S21) <; -35 dB in a reflective environment. The design also has an omnidirectional radiation pattern, reasonable gain values, and a very low envelope correlation coefficient (<;0.001).