A miniaturized phase-inverter rat-race and its wideband Gilbert up-converter is demonstrated in 0.13-μm CMOS technology. The common-mode LO leakage can be absorbed by the isolated port of the rat-race coupler while the rate-race employed at RF port to combine the mixer differential output. A phase-inverter rat-race coupler with a stacked spiral-shape coplanar stripline (CPS) by multi-layer metals can highly reduce the chip size. Finally, the experimental results of up-converter shows the 1-dB conversion gain and 15 GHz RF bandwidth. The IF-to-RF isolation is about 50 dB and LO-to-RF isolation is about 23 dB, respectively.