Planar Multilayer Integrated Asymmetric MIMO Full-Digital Beamforming Array at 24.25–27.5 GHz

This article presents a planar multilayer integrated asymmetric multiple-input multiple-output (MIMO) full-digital beamforming (FDBF) array with “tile-type” at 24.25–27.5 GHz; 32-element transmitting (Tx) array and 16-element receiving (Rx) array are designed and integrated on ten-layer printed circuit board (PCB), in which multichannel up/down converter chips are assembled on top and bottom sides, respectively. The stacked-patch array antenna is divided into <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 4$ </tex-math></inline-formula> subarray antennas and surface mounted on the feeding structure to simplify PCB design complexity. A miniaturized eighth-mode SIW cavity bandpass filter is proposed to provide out-of-band suppression for each radio frequency (RF) channel. To meet the antenna scanning characteristics, RF channels are spaced at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula>/2 intervals at 25 GHz. These channels connect to the array antenna through a feeding structure, while the intermediate frequency (IF) ports are strategically arranged around the edge of the PCB board for convenient connection to the digital baseband. The proposed array operates within the frequency band of 24.25–27.5 GHz, offering a scanning coverage range of ±45° in both azimuth and elevation planes. The measured effective isotropic radiated power (EIRP) of the Tx array achieves 49 dBm at P1 dB. Moreover, the error vector magnitude (EVM) with the 5G NR FR2 400-MHz 64 QAM signal consistently remains below 3% across all scans at an EIRP of 39 dBm. This planar integrated beamforming array effectively addresses the challenge of accommodating a large number of ports in a full-digital MIMO array.