Tunable waveguide filter with bow-tie metallic posts

A waveguide filter employing several conducting cylindrical posts that have a bow-tie shape is synthesised and investigated. The boundary problem of the bow-tie post that is used as a filter section is analysed using an iterative scattering procedure and the orthogonal expansion method. The procedure allows the fast calculation of the modal scattering matrix of the circuit. The shape of the investigated structure, its dimensions, rotation and location in the waveguide junction introduce additional degrees of freedom which can be used to tune the filter so as to obtain the required frequency response characteristic. The rotation of the posts enables the resonant frequency to be slightly changed, which helps to correct any inaccuracies created during fabrication. A good agreement is obtained between the results of this method and those obtained from FDTD simulations and measurements.