This paper presents a miniaturized 10/24-GHz rat-race coupler using synthetic transmission lines on a glass substrate. Compared to a standard CMOS process, the proposed CMOS-compatible glass substrate features lower substrate losses and thicker metal layers. The area-consuming transmission line layouts are implemented by the meandered synthetic transmission lines with high slow-wave factors and low losses. The coupler based on the synthetic TLs is designed, fabricated, and verified. Good agreement between the simulation and measurement is also observed. The chip size is merely 2.5 × 2.2mm² which is comparable to on-chip levels.