Reconfigurable X-Band 4×4 Butler array in 32nm CMOS SOI for angle-reject arrays

Introducing reconfigurable spatial filtering prior to ADC in digital beamforming (DBF) receiver (RX) arrays can improve the RX tolerance for in-band out-of-beam jammers. Such spatial filtering can be achieved using a Butler matrix that provides multibeam outputs. In this paper, an integrated 4×4 reconfigurable X-Band Butler matrix is designed in SOI CMOS to provide multibeam outputs with frequency tunability. The hybrid couplers that constitute the Butler matrix can also be configured to have <;-15dB coupling ratio to create a thru-mode for the matrix. A prototype 4×4 Butler matrix using compact couplers is implemented in 32nm SOI with measured 9GHz to 13GHz frequency tuning range and ~-2.5dB loss per coupler (die occupies 0.64 mm2). Measurements also demonstrate desired multibeam formation and spatial filtering.