150-GHz 28-nm CMOS Reflection-Type Phase Shifter Design Suitable for Low-Q Varactor

This paper presents the design and implementation of a D-band CMOS phase shifter based on a parallel reflective-load topology. Two phase-shifting architectures are explored, namely a 360° continuously tunable phase shifter and a 180° phase shifter combined with a phase inverter, enabling full 360° phase coverage. The circuit was simplified, and the number of bias lines was minimized to facilitate future array circuit implementation. In addition, a serial peripheral interface (SPI) circuit is implemented to simplify bias control and reduce the number of external connections during array chip packaging.