Reactance networks with asymmetrical input and output ports were transformed to an equivalent circuit having an inverter parameter and transmission lines for the purpose of designing band pass filters,structures of the resonators being different from those of the input and output ports.First of all,the reactance network was transformed into a T-section network.And then,according to the F parameter of the T-section network,electrical phases of the transmission lines were formulated by using the reactance elements.Next,an inverter parameter was formulated by open-circuiting the output port of the reactance network.Based on these derived equations,for example,a reactance network consisting of a gap between a coaxial cable and a bi-laterally metal-loaded tri-plate transmission line was transformed to the design diagram for the bi-laterally metal-loaded tri-plate transmission line filter fed by the coaxial cable at 30 GHz.