Synthesis of microwave duplexers using fully canonical microstrip filters

In this work a technique for designing microwave duplexers using two fully canonical filters is presented (that is filters with the same number of reflection and transmission zeros). The proposed approach is based on the exact synthesis of the prototype network of the overall duplexer; in particular the method presented for evaluating the characteristic polynomials of both the duplexer and the composing filters has been suitable extended in order to include characteristic polynomials with numerator and denominator of the same order. The two filters are then synthesized using an inline topology employing non-resonating nodes; the overall duplexer obtained after de-normalization is suitable to be adopted in applications where attenuation requirements are given only in TX and RX channels. A microstrip duplexer designed with the developed procedure confirms the soundness of the proposed approach.