An Edge-Coupled Marchand Balun With Partial Ground for Excellent Balance in 0.13 μm SiGe Technology

An edge-coupled meandered three-coupled-line Marchand balun with a partial ground plane implemented in 0.13 $\mu \text{m}$ SiGe Bi-CMOS technology is presented in this brief. The balance performance of the designed balun is significantly improved by creating a ‘no ground plane’ beneath the coupled-line structure, which is demonstrated by simulating two baluns: one with a partial ground and the other with a solid ground underneath. The measured amplitude and phase imbalances are less than 0.4 dB and 2.5°, across the 3-dB bandwidth from 21.5 to 95 GHz, surpassing previously reported results of edge-coupled Marchand baluns. The balun occupies 230 $\mu \text{m}\,\,\times370\,\,\mu \text{m}$ .