A silicon-based, all-passive, 60 GHz, 4-element, phased-array beamformer featuring a differential, reflection-type phase shifter

This paper presents an all-passive, 4-element, phased-array beamformer based on a differential, reflection-type phase shifter (RTPS) operating in the 60GHz band. The RTPS consists of a differential, vertically-coupled, coupled-line hybrid and variable, parallel-LC, resonant, reflective loads, both of which enable low-loss millimeter-wave operation. The design considerations for a silicon-based implementation of all the beamformer elements are discussed in detail. In particular, the influence of the different RTPS components on its insertion loss is analyzed. The beamformer IC and a breakout of the RTPS are implemented using CMOS-only features of IBM´s 8HP 0.13 μm SiGe BiCMOS process, and employ areas of 2.1mm² and 0.33mm², respectively, without probe pads. Differential s-parameter measurements at 60GHz show a phase-shift range greater than 150°, insertion losses of 4-6.2dB in the RTPS and 14-16dB in the beamformer, and an isolation better than 35dB between adjacent beamformer channels. Measurements across temperature and process variations are also presented.