The integration of thin-film microstrip and coplanar technologies for reduced-size MMICs

This paper proposes the integration of coplanar waveguide (CPW) and thin-film microstrip transmission lines to achieve size reduction of monolithic microwave integrated circuits (MMICs). The proposed structures take advantage of the multilevel metallization processes offered in MMIC technology. A very compact 90° CPW branchline coupler, operating at 44 GHz, is used to illustrate the technique. In comparison with conventional hybrid couplers, this coupler offers lower insertion loss and significantly smaller dimensions. The area of the coupler is approximately 65% of a conventional coupler. This paper also presents a family of novel series/shunt matching stub structures based on the CPW/thin-film microstrip combination. The technique allows a reduction in the length of matching stubs of approximately 50% by collocating multiple stubs together. Simulated and experimental results are presented in support of the novel structures.