Metamaterial-Based Low-Profile Broadband In-Band Full-Duplex Antenna

A low-profile wideband antenna with extremely high isolation is proposed for in-band full-duplex applications. It is designed in a coplanar structure with a periodic array of nonuniform metamaterial cells, a hook-like feeding probe, and four mushroom-like structures. The nonuniform metamaterial cells are excited by a hook-like feeding probe to achieve horizontal polarization. Meanwhile, two slots at the end of the ground are coupled with microstrip feed lines for vertical polarization. As a result, leakage currents between two symmetrical feed structures are suppressed to realize high isolation in wide operation bandwidth. Furthermore, four mushroom-like structures are embedded in the corners of the metamaterial cells to improve bandwidth and isolation. Measured results demonstrate that the proposed antenna with a low profile of 0.06?(0) (?(0) is the wavelength at the center frequency of the operating band) achieves a -10 dB impedance bandwidth of 24.5% from 3.20 to 4.09 GHz and a high Rx/Tx isolation of more than 50 dB. The proposed design has the merits of low profile, wideband, high isolation, and simple feeding structure, which makes it a competitive candidate for in-band full-duplex applications.