Polynomial design of manifold multiplexers

In this work a novel approach to the design of manifold multiplexers is presented, which extend a similar approach previously presented for lumped-junction multiplexers. The filters composing the multiplexer are described through their characteristic polynomials while the manifold network (which may include both lumped and distributed components) is circuit defined. A suitable procedure has been developed for evaluating the characteristic polynomials of the filters and the parameters of the manifold network; in front of the input port of each filter a transmission line section is included, whose length is also computed by the procedure. The design is carried out in the usual low-pass frequency domain; during the numerical evaluations, the polynomials are however evaluated in a suitably transformed domain for increasing the accuracy of the computations. Some design examples are reported in the paper showing the performance of the proposed procedure. A practical duplexer using a star-junction with suitable lengths of transmission line at the input ports of the filters has been designed and fabricated for validation purposes; the measured results shows good agreement with the expectations.