Asymmetric Coupled-Line Directional Couplers as Impedance Transformers in Balanced and $n$-Way Power Amplifiers

Asymmetric 3-dB coupled-line directional couplers for application in balanced circuits have been considered, and it has been theoretically shown that such couplers allow for simultaneous (equal) power division and impedance transformation. A limitation on achievable impedance ratio has been derived. The theoretical analysis has been experimentally verified by the measurements of a number of passive circuits and an exemplary application of the proposed circuits in a four-way power amplifier has been shown.