A Compact <i>Ka</i>-Band 4-bit Phase Shifter With Low Group Delay Deviation

This letter presents a compact Ka-band 4-bit switch-type phase shifter with low group delay deviation (GDD) using 28-nm CMOS technology. A magnetically coupled all-pass network (APN) configuration is employed to achieve both equal and flat group delay characteristics versus frequency at each phase state. The measured rms phase error is 1.2°, and the gain error is 1.1 dB at 33 GHz. The average measured insertion loss is 12.8 dB at 33 GHz, and the input and output return losses are both lower than -10 dB from 29 to 37 GHz. The fabricated phase shifter has a compact size of 0.08 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> excluding pads, low GDD of ±4 ps, and rms group delay error of <; 2.2 ps between 16 phase states from 29 to 37 GHz. The proposed Ka-band phase shifter has the lowest GDD per bandwidth (GDD/BW) compared with other reported passive phase shifters.