LAUSR

In this letter, we present a research on the application possibility of the integrated planar spatial (IPS) combiner in terahertz monolithic integrated circuits (TMICs). The IPS combiner has several attractive characters, such as low loss and good port-to-port isolation. Measured insertion loss of the back-to-back four-way IPS combiner prototype is less than 1.65 dB from 220 to 260 GHz. Then, the IPS power combiner is applied to a four-way six-stage common-emitter InP double heterojunction bipolar transistor amplifier based on a 0.5- $\mu \text{m}$ process. With the help of the IPS combiner and the compact circuit design, this letter greatly improves the output power and output power density compared with other TMICs of the same InP HBT technology. The output power density per unit emitter length (output stage) is 0.51 mW/ $\mu $ m, which is at the same level of amplifiers based on the 0.25- $\mu \text{m}$ InP HBT technology.