Frequency-Tunable 40–44-GHz Butler Matrix

This article details a monolithic microwave integrated circuit (MMIC) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$</tex-math> </inline-formula> switched beamforming feed network, tunable in frequency from 40 to 44 GHz. The completely integrated on-chip Butler matrix is fabricated in the WIN Semiconductors’ gallium arsenide (GaAs) PP10-20 pHEMT process. For frequency tunability, a reflective phase shifter is used in the middle section of the Butler matrix. A fixed-frequency beamforming network is characterized separately at 44 GHz. The reflective phase shifter is also characterized separately from 38 to 46 GHz, as well as over input power. The tunable Butler matrix measurements closely match simulations showing a return loss better than 18 dB and a transmission loss between 3.8 and 6.3 dB in the tuning range. Multibeam performance and leakage are also quantified in simulations, as well as the effects of saturation with increased input power.