In this paper, the design, analysis, and fabrication of a novel coaxial filter based on folded topology are presented. First, two structures of cross-coupling and non-cross-coupling were proposed to achieve the best performance of the coaxial cavity. Second, to reach the smallest dimensions, a folded topology was chosen. Third, phase relationship and also matrix coupling are introduced for determining suitable phase shifts. The proposed method is verified by fabricating a five-order narrow-band coaxial cavity filter for a transverse electromagnetic (TEM) mode at 4 GHz. Finally, the simulation and measurement results of the coaxial cavity filter are presented. Good agreement between simulation and fabrication confirms the validity of the proposed methodology.
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