Introduction
The compound indium phosphide (InP) exhibits exceptional characteristics such as high electron mobility, breakdown electric field, superior anti-irradiation and noise properties, making it extensively utilized in the realm of terahertz integrated circuits. InP HBT/DHBT-based active components and system chips have found diverse applications in terahertz wireless communication, imaging, and radar systems. To establish a parallel relationship between process technology and circuit design methodologies, an accurate model serves as a crucial link. While small-signal models based on InP HBT/DHBT have been widely reported below 100 GHz [1]–[3], there are limited studies that extend their validity up to 200 GHz [4]–[6].