In this video, I show how to use Fest3D to design a dual mode filter. This filter uses cavities connected by irises, with a screw at 45 degrees to couple the horizontal and vertical modes, which allows for a more compact filter.

First, we specify the order and mode of the filter. We can also choose whether to calculate the coupling matrix or import an existing one, and choose an accuracy level for the calculation.

Next, we specify the filter response. Fest3D automatically calculates the coupling matrix as well as the S-parameters for the specified pass band and transmission zeroes.

Finally, we specify the geometric limitations of the filter, such as the radius of the cavity, iris thickness and the screw positions. From this, Fest3D synthesizes a compatible filter.