A miniature 26-/77-GHz dual-band branch-line coupler using standard 0.18-µm CMOS technology

A 26-/77-GHz dual-band branch-line coupler fabricated using standard 0.18-μm CMOS technology is presented. The dual-band coupler is with a compact size of 1.0 × 1.0 mm². The simulated frequency response is to 110 GHz. The measured frequency response shows a good performance with amplitude and phase imbalnce of ± 0.5 dB and ± 5°, respectively, in the low band. The S₂₁ in the high band is about 7.5 dB The measured isolation and the return loss are better than 15 dB within the two passbands. The on-chip coupler will be useful for the integrated design of a 26/77-GHz CMOS single-chip RF transceiver.