Direct-coupled filter utilizing ridge-loaded cavities

A waveguide filter was designed with significant reductions in size and weight and improved out of band spurious levels compared to a conventional filter. The wide bandwidth, high rejection level stopbands required a different approach to a conventional waveguide filter design. Eigenmodes of the ridge-loaded cavity are calculated using Method of Galerkin. The resultant generic structure is used for CAD synthesis of the band pass filter applying Mode Matching Technique. Experimental results are presented for an X-band filter showing good agreement with predicted characteristics. The filter performance is analyzed and compared to traditional design approach showing the advantages of using ridge-loaded cavities.