21.1 A 28GHz CMOS Phased-Array Beamformer Utilizing Neutralized Bi-Directional Technique Supporting Dual-Polarized MIMO for 5G NR

5G NR service will provide extremely-high-speed mobile data access using the millimeter-wave spectrum. To further boost the data-rate and spectrum efficiency, dual-polarized MIMO (DP-MIMO) will be introduced [1-4]. Separated beamformer arrays will be required for H and V polarizations. However, the increased free-spacepath-loss for the 5G NR band n257 (26.5GHz to 29.5GHz) demands numerous elements to cover enough communication distance. Concerning the required considerable number of chips, an area-efficient design will be necessary for a DPMIMO system targeting 5G NR FR2. This paper presents a 28GHz 4H+4V bi-directional beamformer chip supporting DP-MIMO in 65nm CMOS. The proposed neutralized bi-directional amplifier significantly reduces the required on-chip area. A bi-directional vector-summing phase shifter is also introduced. The measured RMS phase and gain errors are 0.4° and 0.2dB at 28GHz, respectively. The array module achieves a saturated EIRP of 45.6dBm/pol. at 0° scan with a 32H+32V array. In a 1m OTA measurement, a 4×4 sub-array module supports single-carrier data-rates of 15Gb/s and 6.4Gb/s per polarization in 640AM and 2560AM, respectively. The measured 400MHz OFDMA TX-to-RX EVM for the 4×4 sub-array module at 0° scan is -34.4dB in 2560AM. 2×2 DP-MIMO communication with a 400MHz 5G NR channel bandwidth is also achieved with a 64-0AM EVM of 4.9% for the 4×4 sub-array module.