This dissertation presents a high-efficiency four-way differential power combiner designed for millimeter-wave and sub-terahertz frequency applications. Conventional Wilkinson combiners and multistage transformer-based structures suffer from increased...
This dissertation presents a high-efficiency four-way differential power combiner designed for millimeter-wave and sub-terahertz frequency applications. Conventional Wilkinson combiners and multistage transformer-based structures suffer from increased metal loss, limited bandwidth, and layout complexity in the D-band, making on-chip integration difficult. To address these limitations, this work proposes a new power-division architecture that combines a transformer-based triport network with a differential two-way combiner employing capacitive loading.
The tri-port transformer is designed by analyzing its magnetic coupling mechanism, including magnetizing inductance, leakage inductance, and mutual inductance, to achieve simultaneous power division and phase balance within a single magnetic structure. The differential two-way
power combiner utilizes capacitive loading to shorten the electrical length of the transmission line, thereby reducing area and minimizing insertion loss. The overall combiner is designed through a combination of circuitlevel modeling and three-dimensional electromagnetic simulations, ensuring wideband operation and excellent phase balance in the D-band. Since on-wafer single-ended probing is required for measurement, a dedicated Marchand balun test pattern is fabricated to independently characterize balun performance, including insertion loss, phase imbalance, and common-mode rejection. The effects of the balun, probe pads, and back-end metal routing are removed through a systematic de-embedding procedure, enabling accurate extraction of the intrinsic characteristics of the proposed four-way differential combiner. The power combiner is implemented in a 65-nm CMOS process. After de-embedding, the measurement results demonstrate an input return loss better than 10 dB from 131 to 154 gigahertz, a minimum insertion loss of 1.89 dB, and a peak port-to-port isolation of 24 dB. The amplitude and phase balance among the four outputs are consistently maintained across the band, validating the effectiveness of the proposed architecture. The results of this study enable a compact and high-performance power-division solution for D-band transmitters, high-resolution imaging radars, and emerging sub-terahertz communication systems. The presented architecture contributes to the development of next-generation millimeter-wave integrated circuit transmitter front-ends requiring wide bandwidth, low loss, and precise multi-path phase alignment.