A 24-GHz CMOS Butler Matrix MMIC for multi-beam smart antenna systems

A 24-GHz 4-way Butler matrix MMIC in 0.18-mum CMOS technology is presented. The multi-layer structure of CMOS process is utilized to monolithically realize the bulky Butler matrix on silicon substrate. Particularly, the multi-layer bifilar transformer is introduced to miniaturize the circuit and reduce the signal loss. The implemented CMOS Butler matrix MMIC only occupies a chip area of 0.41 mm² (excluding I/O pads). The experimental results show that insertion losses are 2.2plusmn0.6 dB from 23 to 25 GHz and the phase errors are within 6deg. Therefore, by connecting this Butler matrix to a linear array antenna, four orthogonal beams, pointing to -49deg, -15deg, 15deg, and 49deg, respectively, are generated within 0.3deg error.