Numerical Coupling Matrix Reconfiguration Methodology for Star-Junction Multiport Networks under AW ladder constraints

This work generalizes a matrix-completion–based reconfiguration methodology to the synthesis of star-junction multiplexers under AW ladder constraints. Starting from a transversal multiport canonical coupling matrix, a congruent transformation is performed that simultaneously removes all direct port-to-port couplings, creates a common star node that connects to each channel through evenly distributed admittance inverters, and enforces frequency-invariant reactance (FIR) constraints at the external ports to control the phases of the first/last extracted-pole sections in every branch. The transformation matrix is solved as a structured matrix completion problem with a projected-gradient method, extended to keep the conductance matrix invariant and to encode star-junction and ladder sign-pattern constraints in block-structured projection masks. The approach preserves the target frequency response, admits matrix size augmentation, and directly yields dangling in-line multiport networks in the prototype domain. A B3Tx–B1Rx duplexer example serves as a proof-of-concept to validate the methodology.