Embedded Near-Field Probing Antenna for Enhancing the Performance of 37–41-GHz Linear and Dual-Polarized Phased Antenna Arrays

This letter proposes a new wideband near-field (NF) probing antenna embedded in millimeter-phased antenna arrays to produce the feedback signals necessary for carrying-out array calibration and digital pre-distortion (DPD) training. Specifically, the topology and layout of the proposed NF probing antenna are carefully devised to avoid disturbing the antenna array’s radiation pattern while providing a coupling to its surrounding antenna elements with flat magnitude and constant group delay in both vertical and horizontal polarizations. Moreover, the proposed NF probing antenna size is optimized to cope with the constrained spacing between the antenna elements (e.g., $\lambda b /2$ antenna spacing). Proof-of-concept prototypes of a $2 \times 2$ dual-polarized passive and a $4 \times 4$ linear-polarized active antenna arrays with embedded NF probing antenna(s) operating over the frequency band of 37–41 GHz were designed. Moreover, a $4 \times 4$ linear-polarized antenna array without NF probing antennas was also fabricated to serve as a benchmark. The measurement confirmed the negligible impact of the NF probing antennas on the antenna array’s radiation pattern. Furthermore, the embedded NF probing antennas were successfully used to train a DPD function which then enabled the effective isotropic radiated power to be increased from 32 to 34.1 dBm while maintaining an error vector magnitude (EVM) below 3.5%.