A Miniature 92–95 GHz On-Chip Slow-Wave Branch-Line Coupler

A miniature 92–95 GHz on-chip branch-line coupler (BLC) employing a slow-wave microstrip line is proposed herein. The ground metal plane beneath the signal line is periodically slotted, and the coupler can be highly miniaturized owing to the short wavelength characteristic of the transmission line with slow-wave structure. The size of the slow-wave BLC is $\mathbf{250 \ \mu m\times 250\ \mu m}$ , which is 39% of the size of conventional BLCs.