A 220–340 GHz Modified Marchand Balun With Asymmetric Ground Shield in 90-nm SiGe-BiCMOS

Abstract

This work presents a modified Marchand balun for sub-terahertz frequencies. By introducing an asymmetric ground shield in the coupler sections, low imbalance is achieved at the differential port. The proposed design is well-suited for on-wafer testing of differential power amplifiers and antennas. A prototype fabricated in a 90-nm SiGe-BiCMOS process is characterized in the 200–325 GHz range, showing good agreement with simulations. The measured amplitude and phase imbalances at 270 GHz are 0.1 dB and 2.5°, remaining lower than ±1 dB and 3.5° in the 240–290 GHz frequency range. The measured insertion loss is below 2.5 dB, while the simulated return loss in the single-ended port is better than 10 dB in the 220–340 GHz range.