Series-configuration of multi-line directional-coupler sections with improved coupling

Different from well known conventional designs of parallel-multi-line directional couplers, this paper presents methods to substantially increase the coupling of parallel-line coupler types. Higher coupling is achieved by a novel series configuration of two coupler elements, with moderate, individual coupling, and additional phasing lines in between these two coupling elements. Additional coupler elements allow for broadband designs. Besides high coupling, in principle this coupler arrangement yields substantial decoupling of output ports. This paper presents the basic for three-parallel-line systems and shows simulation results verified by measurements.