A novel approach to dual and triple-mode pseudo-elliptic filter design

A novel approach to dual and triple-mode pseudo-elliptic filter design is introduced. Instead of using the degenerate modes of a physical resonator, non-degenerate ones are used instead. All the coupling coefficients are positive (their signs are inconsequential). All intra-cavity couplings are eliminated. Each transmission zero is generated and controlled by a dedicated mode whose resonance frequency coincides with the frequency of the transmission zero. The design is ideal for situations where real transmission zeros are required in the immediate vicinity of the passband. A triple-mode rectangular cavity filter with two transmission zeros is designed, fabricated and measured to demonstrate the validity of the approach.