A 26.5-GHz 4x2 Array Switched Beam-Former Based on 2-D Butler Matrix for 5G Mobile Applications in 28-nm CMOS

This paper demonstrates a 26.5-GHz 2-D Butler matrix based 4×2 array switched beamformer. By using a 2-D Butler matrix, feed lines between IC and antennas are uniform, which is a critical problem in an integrated Butler matrix for a 1- D array since it requires complex phase matched routing on PCB. A proposed switched beamformer consists of a signal distribution IC and two switched beamformer ICs. Reconfigurable switches with a function of power divider/combiner are integrated for additional beam patterns. The proposed switched beamformer can generate total 22 beams, which cover a whole scan angle with a low gain variation. Measured beam patterns show that the proposed switched beamformer can cover any 3-D spatial angle of ±44° in azimuth and ±43° in elevation even with a low spatial beam resolution. To our knowledge, this is the first 2-D array switched beamformer based on the Butler matrix in millimeter wave bands.