Diplexer design using pre-synthesized waveguide filters with strongly dispersive inverters

An approximate synthesis technique for strongly dispersive inverters is introduced. The technique allows the prescription of transmission zeros at finite frequencies on either side of the filter passband - symmetrically or asymmetrically - as required for diplexer applications. Several direct-coupled resonator filters with additional attenuation poles and a related diplexer design at 18.5 GHz are presented. The computerized design procedure is based on CIET (coupled-integral-equations technique) and MMT (mode-matching technique) modules. Excellent agreement between measurements and theoretical predictions is achieved.