This paper presents a 4-element 44-GHz Butler matrix implemented in a single GaAs chip. The 90° 3-dB couplers are implemented with two coupled line sections, and the tunable phase shifters allow for frequency tuning from 40–44GHz with a 1-V bias change. The reflective phase shifters are implemented with tunable HEMT reactances on two of the ports. The simulated and measured progressive phase profiles are in good agreement, with less than 6° error for 4 available beams from 40 to 44GHz.
