Beam Defocus in Near-Field Wideband Cylindrical Antenna Array Systems: Analysis and Mitigation

In this letter, a near-field wideband cylindrical antenna array (CLA) system is studied. By deriving the transmitted beam gain, we characterize the beam defocus effect in the system. Then, based on the geometry of CLA, we decompose beam defocus in the CLA system into a combination of beam defocus in circular arrays and beam squint in linear arrays. To mitigate the CLA beam defocus, two precoding architectures are proposed, namely the fully-connected true time delay (TTD) architecture and two-stage delay-phase-precoding (DPP) architecture. Simulation results show that our proposed architectures can alleviate the hardware overhead and effectively mitigate beam defocus.