High Resolution Reconfigurable Phase-Tuning Line Using Self-Shielded 3-D Interdigital Capacitor

A compact high-resolution reconfigurable phase-tuning line (RPTL) based on self-shielded 3-D interdigital capacitors is presented in this letter. Such a capacitor with high-$Q$ and self-shielded characteristics is used to implement the digitally switchable capacitor array in the RPTL, which is integrated with a coplanar waveguide and can lead to merits of the low loss, high phase-tuning resolution, and compact size. Meanwhile, the grounded shield is utilized in the RPTL to further reduce the loss. To verify the mechanisms of aforementioned structure, a 6-bit digital controlled RPTL is implemented and fabricated using a 40-nm CMOS technology. At 30 GHz, the measured loss of the proposed RPTL is 2.1 dB, while a tuning resolution of 0.38° with an RMS phase error of 0.25° is achieved.