Self-Packaged Slow Wave Metal-Integrated Coplanar Waveguide (MICPW) for Compact Branch-Line Coupler Design

This article proposes a slow wave metal-integrated coplanar waveguide (MICPW) with low loss and self-packaging. Since almost no substrate is used for the MICPW, there is almost no dielectric loss. The signal trace of the MICPW is embedded inside the multilayer metal boards, the overall circuit is self-packaged and there is almost no radiation loss. The slow wave effect is generated by using the shunt stub. The proposed slow wave MICPW is utilized to design compact branch-line couplers. Two types of supporting structures for the suspended metal lines are presented. Two design cases operating at 3.5 and 1.8 GHz are implemented, and the core circuit areas are $0.13\lambda $ g $\times 0.26\lambda $ g and $0.14\lambda $ g $\times 0.17\lambda $ g, which shows a size reduction of 46% and 62% compared to the traditional counterparts. The measured loss percentages are only 3% and 1.14%, which are much smaller than that of the other reported works.