Coping with hidden spurious harmonic modes in the design of low pass corrugated waveguide filters

Hidden spurious harmonic modes in corrugated waveguide filters are investig ated from both theoretical and practical points of view. It has been found that multiple mode couplings occurring, at more than one place in a filter system cause the hidden spurious modes. An effective simulation scheme is i ntroduced here to predict the hidden spurious modes based on a logical and methodical physical interpretation. The theoretical mechanism and proposed simulation scheme are both validated through a direct measurement and full- wave electromagnetic simulation.