Abstract
A 4×4 Butler matrix for millimeter-wave communications is presented in this paper. The circuit takes advantage of a new 3-D Integrated Passive Devices (IPD) process to achieve a performance/compactness trade-off substantially higher than conventional IPD designs. A footprint of 0.84mm2 is reached by using 3-D transformers and solenoids for designing couplers and phase shifters. Couplers are optimized to maximize the bandwidth of the Butler matrix. Phase variations with frequency are also tuned between phase shifters and crossover for the same purpose. The resulting experimental bandwidth, defined by reflection coefficients at −10 dB, is from 20GHz to 30.1GHz, and from 22.1 to 27.5GHz considering a maximum phase error of 10° for the four states −45°, 135°, −135° and 45°, while insertion losses are measured close to 1.3dB. Matchings and isolations remain below −17 dB and −12 dB, respectively.
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