Compact CMOS branch-line coupler using high-Q slow-wave transmission lines

Abstract

This article presents a miniaturized 90° coupler incorporating slotted conductor-backed coplanar waveguide (S-CBCPW) transmission lines (TLs) and four shunt capacitors. The periodically slotted ground achieves higher slow-wave factor (SWF) or effective permittivity (εeff), and lower attenuation constant. Electrical characteristics of the S-CBCPW TLs are investigated by different slotted ground layers. Moreover, trade-offs among SWF, characteristic impedance, and electrical length for the design are also discussed. Finally, the measured 24-GHz coupler not only features smallest normalized chip area among previously reported CMOS couplers but also demonstrates excellent results which are comparable to the designs at 60 GHz. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1174–1178, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27525