Design of ultra compact pseudo-elliptic inline waveguide bandpass filters using inductive bypass coupling for various specifications

In this paper, practical implementation aspects of recently proposed ultra compact inline waveguide bandbass filters that utilise stoband performance of their pseudo-elliptic responses through positive sign bypass coupling are explored. Fundamental working principles are outlined from different perspectives and a number of X band filter samples are described in details, together with fabrication process using a pair of thin metal inserts positioned parallel along two different E-planes of a straight waveguide section. Developing from the core strengths of compactness, being 70% smaller than conventional E-plane filters, and ease of fabrication, discourse is continued by exposing the filters to different application challenges. It is demonstrated that the proposed structure is not only suitable for narrowband designs, giving a sample of a filter with 12% fractional bandwidth, still maintaining dimensions that allow fabrication with the same machining equipment. In addition, flexibility of producing the same filter response by modifying dimensions of different elements is shown. Sensitivity analysis is carried out and an approach to fine mechanical filter tuning is proposed. Furthermore, an example of higher degree filter of the fifth order is presented to illustrate the ability of the filter to meet demanding real-life specifications.