Millimeter-wave Diplexer

A rigorous field theory analyse of one kind of rectangular waveguide H-plane diplexer is described. E-plane band-pass filter and waveguide H-plane T-junction are the most important parts of the diplexer. Since equivalent-circuit method can bring more error, we use mode-match method and make the computation program for the optimization of the E-plane metal-insert filter. The immediate higher order mode coupling between the discontinuities, which reduces the stop-band attenuation for higher frequencies and the influence of the finite thickness of the metal inserts, which influences pass-band ripple behavior and mid-band frequency are taken into account in the mode-match method. The computation result fits the data in literature well. The discontinuity of T-junction can be compensated by an inserted metal iris, the broadness and insert deepness of the iris can be achieved by optimization using FEM software. From the simulation result we can see that the waveguide T-junction achieves good matching in wide frequency band. The S-parameters of the H-plane diplexer can be deduced by combing the scatter matrix of E-plane band-pass filters and T-junction. The distances between the filters and T-junction are also optimized.To realize the design target, the efficiency optimization methods are necessary. we use genetic algorithm and simplex method in this article. The theory is verified by measured results for Ka-band E-plane filters and diplexers. The measured insertion loss of the E-plane filter in the passbands is about 0.98dB at 37GHz and 0.49dB at 38.5GHz, and the insertion losses are 2.17dB in the 36.75 to 37.25GHz channel and 2.44dB in the 38.25 to 38.75GHz channel of the Ka-band diplexer.