Design of In-Line Dual-Mode Rectangular Waveguide Bandpass Filters Using Multiple Inductive Circular Posts

In this paper, the concept of utilizing circular inductive posts as a simple inductive discontinuity coupling method for the implementation of in-line dual-mode rectangular waveguide filter is introduced. The use of shunt inductive posts facilitates the fabrication process and reduces filter size/weight if compared to other dual-mode inductive coupling methods. The complete design procedure of the proposed structure is introduced. The proposed filter concept is validated by application examples which are fabricated and measured. Experimental results indicate excellent agreement with theory. This is the first reported in-line "all-inductive" dual mode microwave filters applying multiple circular posts for coupling to the best of the authors' knowledge.