Broadband substrate integrated coaxial line to CBCPW transition for rat-race couplers and dual-band couplers design

Abstract

In this paper, broadband transitions from substrate integrated coaxial line (SICL) to a conductor-backed coplanar waveguide (CBCPW) are proposed and designed. Measurement results show that the insertion loss and return loss are better than - 0.5dB and -10dB, respectively from 0 to 13GHz. Then, for verifying the performance of SICL and the validity of SICL transition design, a 3dB SICL rat-race coupler operating at 2.3GHz is designed, fabricated, and measured. Compared with the conventional microstrip line coupler, this SICL coupler maintains good performance but with a remarkable 24% reduction in size. At last, a 10dB dual-band coupled SICL coupler operating at 2.4/5.8GHz is proposed, and the measured results agree well with the schematic and electromagnetic simulated results. The measured results demonstrate that the fabricated bandwidths are 30% and 12.8%, the {pipe}S31{pipe} are -10.1dB and -10.3dB, the directivities are 18dB and 20dB at the low (2.4GHz) and high (5.8GHz) operating frequencies, respectively. Compare with the dual-band coupled microstrip line coupler, performance of the dual-band coupled SICL coupler is enhanced.