A Wideband Phased Array RF Front End With Coupling-Capture Channels for Full-Duplex Wireless Backhaul

Wideband full-duplex (FD) phased arrays are expected to deliver substantial traffic capacity, spectral efficiency, and flexible beam steering for wireless backhaul applications. However, significant self-interference (SI) from the transmitter (Tx) to the receiver (Rx) poses a major obstacle in enabling FD communication. This article proposes a new phased array architecture to address this issue by utilizing staggered Tx and Rx antenna arrays with an additional coupling-capture (CC) channel in the Rx. The complex and frequency-dispersive coupling characteristics between the Tx and Rx arrays can be effectively captured for RF SI cancellation (SIC) throughout a wide spectrum with diverse scanning angles while preserving the desired receiving signal. Then, a multipeak RF canceller is employed to enhance the SIC level with fewer components and simpler control compared to prior approaches. The proposed phased array was demonstrated using a 1-D Vivaldi antenna array with six transmitting and six receiving elements, operating across 0.8–1.5 GHz. The Tx and Rx arrays are placed with a separation of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.13\lambda _{\text {L}}$</tex-math> </inline-formula>, allowing them to share a common aperture. A 2-D array may be readily developed from the 1-D array with an antenna aperture size comparable to that of a traditional half-duplex (HD) phased array. Measurements show that the proposed phased array realizes a 48.6-dB SIC throughout a scanning range of ±30° when the maximum transmit equivalent isotropic radiation power (EIRP) exceeds 30 dBm. Moreover, the SIC technique neither degrades the system’s ability to receive desired receiving signals nor elevates the Rx noise figure (NF).