Decoupling of Closely Spaced E-Plane In-Band Full-Duplex Patch Antennas with Via-Loaded U-Shaped Strips for Vehicular Communications

Targeting sub-6 GHz in-band full-duplex (IBFD) communication applications covering the vehicular Intelligent Transportation System (ITS) band (5.85–5.925 GHz), this article proposes a phase-guided path-cancellation decoupling method for closely spaced E-plane transmit/receive (Tx/Rx) patch antennas. In this method, the phase of the original coupled signal is first extracted at the target frequency. Then, an additional coupling path with an opposite phase to the original coupling channel is introduced to suppress the strong E-plane mutual coupling. Based on this method, compact via-loaded U-shaped strips are employed to realize decoupling, achieving high port isolation without increasing the antenna profile. Simulated and measured results show that the proposed antenna achieves a port isolation of 20–36.6 dB over 5.72–6.07 GHz, corresponding to an operating bandwidth of 5.9% and a mutual-coupling improvement of 11.5–28.1 dB. Meanwhile, the antenna maintains a low profile of 0.059λ0and a compact edge-to-edge spacing of 0.04λ0, while the U-shaped decoupling structure has an overall length of approximately one-quarter of the effective wavelength, indicating its suitability for compactly integrated IBFD Tx/Rx patch arrays.