A 28-GHz 2×2 Antenna Array Integrated with a Butler-Matrix Beamformer IC Based on AiP Technology

This work demonstrates the integration of a 2 × 2 wideband antenna array and a beamformer IC based on Antenna-in- Package (AiP) technology using a 10-layer organic substrate with dimensions of 13 × 13 × 0.87 mm³. The antenna elements employ a stacking patch technique, with simulations determining the optimal stacking ratio to enhance cost-effectiveness. To broaden the operating bandwidth, four parasitic patches were used into the design. The antenna array achieves a return loss of 10-dB over the frequency range of 23.7 to 32.3 GHz, with element gain between 4.8 and 5.4 dBi at 28 GHz. In addition, the AiP integrates a four-way Butler-matrix beamformer IC designed in 90-nm CMOS process, enabling two-dimensional (2-D) beamforming capabilities. To evaluate the performance of AiP, a customized test fixture was fabricated and used in the compact antenna test range (CATR) system. Measured 2-D beamforming gain is from 16.1 to 18.0 dB at 28 GHz. The results demonstrate a good correlation between simulation and measurement, confirming the effectiveness of this compact AiP for millimeter wave (mmWave) applications.