I. Introduction
The last few years have witnessed a surge in Sub-millimeter and terahertz integrated circuits mainly for InP based heterojunction bipolar transistor (HBT) has been shown to have maximum frequencies of oscillation (fmax) over 1 THz [1]. In terahertz wave bands, InP devices are the preferred choice because its superior characteristics, such as high electron mobility, high withstand power and high radiation resistance. InP DHBT devices with a higher breakdown voltage and high output power at a specific current gain cutoff frequency (ft) [2], [3]. H-band (220 GHz - 325 GHz) is well suited for interstellar communications and imaging radars applications [4]. In recent years, with the 0.25um and 0.15um InP DHBT technology development, many W-band, G-band and H-band power amplifiers are reported [5], [6].