THE DESIGN OF SINGLE-SECTION AND WIDE-BAND SYMMETRICAL 3-LINE MICROSTRIP COUPLERS

The three-line microstrip coupler consists of three parallel strips on a dielectric substrate above a ground plane. The six-port network com bines a specified fraction of two independent input signals on a commo n conductor without interaction of the signal sources. The results of a quasi-TEM analysis of the three-line coupler ave used to accurately predict the scattering parameters of a structure of arbitrary linewidt hs and section length. A search for suitable dimensions of couplers th at meet certain design criteria is performed, with the use of a modeli ng technique that relates the six-port network to two simple circuits. The results are set design curves, which are used to design both a si ngle-section coupler and a wideband stepped coupler. The theory is val idated through comparison with experimental data for the manufactured prototypes. (C) 1996 John Wiley & Sons, Inc.