A 4.5–5.5-GHz Compact 6-bit Phase Shifter With Low RMS Phase and Amplitude Errors Based on Bandpass Structure for High-Power Applications

This article presents a compact 6-bit digital phase shifter (PS) monolithic microwave integrated circuit (MMIC) with low root-mean-square (rms) phase and amplitude errors. A novel bandpass phase-shifting cell (PSC) with embedded high-isolation switches is proposed and adopted in 180°- and 90°-bit designs to compensate the isolation-degradation caused by the large drain-source capacitance of GaN transistors. Then, a systematic design method is investigated to minimize phase and amplitude errors. To validate the proposed techniques, a 6-bit C-band PS is implemented in a$0.25~\mu $m GaN-on-SiC HEMT process with a circuit size of$1.9\times 2.5$mm2 ($0.03\times 0.04\lambda ^{2}$). The measured rms phase error of the proposed PS is less than 1.2° from 4.5 to 5.5 GHz with a 2.8° calibration bit. The insertion loss (IL) varies between 5.8 and 8.2 dB with an rms amplitude error of less than 0.5 dB. Besides, a good power linearity with 37.9 dBm input 1 dB compression point (IP$_{\mathrm {1\,dB}}$) and 49.8 dBm input third-order output-referred intercept point (IIP3) is also attained. The proposed PS exhibits superb overall performances in phase resolution, phase/amplitude error control, IL, and power handling capability within a small chip size. It can be a potential candidate for various systems including radars, cellular base stations, and avionic devices.