A 44-GHz 4×4 MMIC Butler Matrix

A 44 GHz Butler matrix designed and manufactured in an InGaAs MMIC process is presented. A compensated crossover is designed to effectively use the two metal layers available in the process while limiting coupling and mismatch to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{- 3 0} \text{dB}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{- 2 8} \text{dB}$</tex>, respectively. The phase shifts are implemented with multiple coupled-line sections and couplers as tandem couplers. On-wafer measurements on a 2.5 mm by 2.5 mm chip show an insertion loss of 2.4 dB and match better than 16.5 dB with amplitude imbalance and phase error of 1.5 dB and 10.8° at 44 GHz. The multiport measurements are enabled with reconfigurable on-chip terminations at the ports. A narrowband patch antenna array on Rogers RT/Duroid 5880 is designed, and the simulated array patterns using the Butler matrix as a feed network are also shown for both single beam and multi-beam performance.