A 10-40 GHz 7 dB Directional Coupler in Digital CMOS Technology

We present an integrated wideband directional coupler for millimeter-wave applications implemented in low-cost silicon technologies. It is constructed using broad-side coupled coplanar waveguides (CPW), taking advantage of available multiple metal layers in silicon technologies. A prototype coupler was designed and fabricated using a commercial 0.18mu digital CMOS technology with low-resistivity epi substrate. It achieves a 10-40 GHz frequency range (3-dB bandwidth) with 7 dB to 10 dB coupling and more than 10 dB directivity. Measurement results match well with electromagnetic simulation