Design of triplexer combiners for base stations of mobile communications

This work presents a design technique for a class of combining networks used in base stations for mobile communications; the considered network is a triplexer composed by three high selectivity filters presenting arbitrary transmission zeros (both complex and pure imaginary), which are connected at the input port through a suitable 4-port junction. A technique for the design of this combining network is here proposed, which extends a previous approach used for duplexer networks. The design consists in a procedure for the evaluation of the characteristic polynomials of the three composing filters (defined in a normalized frequency domain), once the input junction topology and the transmission zeros of the filters have been assigned. The network synthesized from the characteristic polynomials presents the same reflection zeros of the three filters synthesized separated from the triplexer with an equiripple response in their respective passband; in this way the overall synthesized triplexer presents a quasi-equiripple response in the three passbands. The proposed design approach has been verified through a fabricated prototype, whose measured performance is in good agreement with the expected response obtained from the synthesized network.