Symmetrical In-Band Full-Duplex Antenna With Broad Bandwidth Using Stacked Patch Array

This article proposes a novel symmetrical design for a Broadband Bidirectional In-band Full-duplex (IBFD) co-radiator antenna with high isolation. The distinctive double differential feed network, constructed using orthogonally arranged meander slot baluns, is connected to a pair of co-radiating patches with the metallic visa, resulting in structural symmetry and offering bidirectional radiation patterns. The null-coupling features of the balun, that is, the differential potentials and differential filtering, generate good isolation in the antenna with a narrow bandwidth. The limitation of narrow bandwidth has been overcome by employing a stacked patch array above the radiating patch. The installed $2\times 2$ stacked patch array generates additional resonating modes due to the induced surface waves and enhances the operational bandwidth of the antenna. The multiple techniques of polarization diversity, double differential feed, and stacked patch array in the antenna offer a minimum isolation of 62 dB over a wide operational band of (1.8–2.9) GHz. It offers bidirectional broadside radiation having a lower cross-polar of $<-25$ dB. Moreover, the structural symmetry of the antenna produces identical S-parameters, gain, and radiation patterns for both antenna ports. The fabricated prototype of the proposed antenna with overall dimensions of $\left(0.66\times 0.66\times 0.122\right){\lambda }_{\text{min}}$ (${\lambda }_{\text{min}}$ is the free space wavelength referring to the lowest operational frequency) shows a good correlation between the simulated and measured results.