Symmetric solutions of problem of synthesis of three-link stepped microwave filter of Butterworth

It is demonstrated, that the problem of synthesis of three-link stepped microwave filter of Butterworth has two symmetric solutions. These solutions have equal wave impedances of the first and last links. The first solution corresponds to filter configuration with low-resistance central link. The second solution corresponds to configuration with high-resistance central link. The expressions for wave impedances of filter links are derived. The results of computation of wave impedances are brought.