Isolation Enhancement Between Two Low-Profile Patch Antennas for In-Band Full-Duplex Applications

An enhanced isolation technique between two low-profile patch antennas is proposed. Two identical antennas are configured with two PCBs spaced at 0.206 λ ₀ , where λ ₀ is the free-space wavelength at 3.5 GHz. Every antenna is a rectangular patch with four slots and two vias, vertically fed with a coaxial probe. A decoupling strip embedded between two antennas and a slot on the ground improves isolation, which would not deteriorate the cross-polarization and backward radiation levels. Two-port impedance match and isolation characteristics are analyzed when the two-antenna spacing varies from 0.159 λ ₀ to 0.252 λ ₀ . The proposed antenna has a size of 0.817 λ ₀ × 0.448 λ ₀ × 0.038 λ ₀ . The fabricated prototype is measured, and the results demonstrate that the -10 dB impedance bandwidths are 3.37–3.61 GHz (6.88%), the port-to-port isolation is more than 45.2 dB, the realized gains are 4.53 ± 0.35 dBi, and the average radiation efficiencies are more than 70%. Therefore, the measured results agree well with the simulated, making it a promising candidate for in-band full-duplex applications in 5G terminal scenes.