A Stability-Enhanced X-Band 6-Bit Digital Phase Shifter With Low RMS and Absolute Phase Error for High-Precision Tracking Radars

High-precision tracking radars demand accuratephase and amplitude control to ensure reliable target detectionand tracking, as small errors can significantly degrade systemperformance. This paper presents a stability-enhanced 6-bit dig-ital phase shifter (DPS) operating from 9.3-10.5 GHz, fabricatedin a 65 nm CMOS process. A modified coplanar waveguide(CPW) transmission line (TL) on the top metal layer (M9),with a 4.7 \u03bcm signal trace and 2 \u03bcm air gap, is implementedto optimize radio frequency (RF) performance. To ensure robustoperation across all states, a switchable phase-selective stability(SPSS) circuit is introduced between phase control blocks. TheSPSS dynamically inserts a stabilizing pole when the phase stateapproaches instability regions, improving overall stability. Thechip occupies 0.916 mm\u00b2 and is packaged in a 4 \u00d7 4 mm QuadFlat No-Lead (QFN) package. Measured results show root meansquare (RMS) phase error < 2.2\u00b0, with an absolute phase error\u2264 4\u00b0 for 97.84% of states. The proposed design exhibits aninsertion loss of 11.05 \u00b1 3.15 dB, an RMS amplitude error lessthan <1.74 dB, and a reflection coefficient below -10 dB across theband. These results demonstrate its suitability for high-precisiontracking radar systems.