Design of Multisection Asymmetric Couple-line Couplers with Rotated Tightly-coupled Section and Reduced Coupling Coefficient Requirements

A novel solution of broadband asymmetric multisection coupled-line directional couplers has been proposed in which the required coupling of the tightly-coupled section is reduced. The coupling coefficient reduction has been achieved by the appropriate connection of a tightly-coupled section which has been rotated and connected with the remaining sections in such a way that the transmission and coupled ports are interchanged. It has been shown that in such circuits it is possible to achieve equal-ripple coupling characteristics similar to the classic multisection asymmetric coupled-line couplers. The numerical calculations of the proposed couplers have been performed and the obtained results are presented in a tabular form. The presented concept has been confirmed by measurements of the manufactured three-section asymmetric coupled-line directional coupler operating in the frequency range 0.5-2.5 GHz.