Novel design of a 2.5-GHz fully integrated CMOS Butler matrix for smart-antenna systems

This paper presents a novel design of monolithic 2.5-GHz 4 x 4 Butler matrix in 0.18-mu m CMOS technology. To achieve a full integration of smart antenna system monolithically, the proposed Butler matrix is designed with the phase-compensated transformer-based quadrature couplers and reflection-type phase shifters. The measurements show an accurate phase distribution of 45 +/- 3 degrees, 135 +/- 4 degrees, -45 +/- 3 degrees, and -135 +/- 40 degrees with amplitude imbalance less than 1.5 dB. The antenna beamforming capability is also demonstrated by integrating the Butler matrix with a 1 x 4 monopole antenna array. The generated beams are pointing to -45 degrees, -15 degrees, 15 degrees, and 45 degrees, respectively, with less than 1 degrees error, which agree very well with the predictions. This Butler matrix consumes no dc power and only occupies the chip area of 1.36 x 1.47 mm(2). To our knowledge, this is the first demonstration of the single-chip Butler matrix in CMOS technology.