A Novel Reduced-Size Rat-Race Broadside Coupler and Its Application for CMOS Distributed Sub-Harmonic Mixer

A broadband distributed sub-harmonic resistive field effect transistor mixer with a novel modified rat-race broadside coupler using a 0.13-$\mu{\rm m}$ CMOS foundry process is presented in this letter. Using the broadside coupler, a reduced-size rat-race is fabricated with a compact size of 110$\, \times \,$80 $\mu {\rm m} ^{2}$. From the measurement results, the mixer achieved a conversion loss of 12 dB from 32 to 70 GHz of RF frequency. The passive sub-harmonic mixer has zero power consumption. With the modified rat-race broadside coupler, the mixer achieves a good LO-IF isolation of better than 30 dB and a compact core chip size of 0.55 $\, \times \,$0.4 ${\rm mm}^{2}$.