CMOS 4×4 and 8×8 Butler matrices

This paper presents miniature Ku-band 4 × 4 and C-band 8 × 8 Butler matrices in a 0.13 μm CMOS implementation. The 4 × 4 design results in an insertion loss of 2.4 dB at 12 GHz with a bandwidth of 11-13 GHz. The chip area is only 0.85 ×0.65 mm² including all pads, and the power consumption is ~0 mA from a 1.5 V power supply. The 4 × 4 matrix is mounted on a Teflon board with 4-antennas, and the measured patterns agree well with theory and show an isolation of > 11 dB at 11-13 GHz. The work is also extended to an 8 × 8 Butler matrix at 5-6 GHz and with excellent performance. CMOS Butler matrices are an excellent candidate for MIMO systems, and can also replace small-element phased-array systems for high-gain transceivers. The applications areas are in high data-rate communications.