The Canonical Coupler : A New Approach to Microwave Coupler Design

Abstract
Mutually coupled transmission lines are described by inductance and capacitance matrices. Such a system can be reduced to a canonical matrix form which provides the basis for a new design technique. Expressions are given for the scattering parameters in terms of the line parameters enabling realisable couplers to be designed. To demonstrate the technique 2 GHz comb and herringbone line couplers are constructed with nearest neighbour interaction in the capacitance matrix and a diagonal inductance matrix. At present a two-line codirectional coupler and a three-line balun, both with equal power division, have been successfully constructed.