A Synthesis-Based Design Procedure for Waveguide Duplexers Using a Stepped E-Plane Bifurcated Junction

A novel design procedure for waveguide duplexers using stepped E-plane bifurcated junctions is presented. First, a simple model of this junction is devised, suited for the synthesis of star-junction diplexers (a novel procedure has been developed). The characteristic polynomials of the channel filters obtained by this procedure are then employed for the synthesis of the channel filters. To allow transmission zeros in the response, an in-line topology with frequency-dependent (resonant) couplings is adopted. The filters are synthesized with a recently proposed technique (here adapted for waveguide implementation). Furthermore, a new type of resonating coupling structure is adopted (the stopband singlet), allowing the positioning of the transmission zeros very close to the passband. The novel design technique is demonstrated with a Ka-band duplexer for satellite applications.