Wide spurious free range positive-to-negative inter-resonator coupling structure for reconfigurable filters

A structure for positive-to-negative inter-resonator coupling in cavity resonator filters is shown in this paper. Mechanically and electrically reconfigurable versions of the structure are described. The structure has a wide spurious free range while retaining the capability to provide near-zero coupling because it uses symmetry to redirect digitally addressable amounts of current to adjust coupling values instead of using the phase shift through a resonance. It is applied to 6-resonator cross-coupled filters whose response can be adjusted between several different orders and shapes, including shapes with and without transmission zeros. A technique for improving the near-zero coupling state is also presented.