A Cascaded Self-Similar Rat-Race Hybrid Coupler Architecture and its Compact Fully Integrated Ka-Band Implementation
This paper presents a cascaded rat-race coupler architecture that performs broadband in-phase and differential signal generation while maintaining a very compact passive structure size. Our proposed cascaded coupler can support multi-band multi-standard 5G communication systems at 24, 27, 37, 39GHz. We have demonstrated that the cascade topology successfully suppresses the output amplitude mismatch and maintains differential output phases, enabling substantial coupler bandwidth extension. A proof-of-concept 22.6–43.4 GHz 2nd-order cascaded rat-race coupler is implemented in the GlobalFoundries 45nm CMOS SOI process. Based on our measurement results, the cascaded rat-race coupler design achieves a less than 5° phase error, less-than 1dB magnitude mismatch, an average insertion loss of only 2.5dB, and better-than -10dB input matching across the entire Ka-band.