An improved design of systems based on three coupled microstriplines

The design parameters of three coupled equal-mode-impedance microstrip lines on an alumina substrate are introduced in a manner that gives a convenient systematic design procedure. The use of equal-mode-impedance lines greatly facilitates the design of the system. The design procedure for two configurations of this system is presented. A coupler satisfying the requirements of one of these configurations is realized and its practical performance is shown to be in good agreement with theory. The design procedure is applicable to any such system on any other isotropic substrate material