Effect of conductor losses in new‐structure filters for suppressing microwave leakage

As a waveguide-type broadband elimination filter preventing leakage from a microwave heating system, a waffle-iron type filter is known which consists of a periodic structure of a multiple post structure with many circular or rectangular cylindrical metal posts placed periodically inside a waveguide. The theoretical analysis of this filter has been limited to the case in which the conductor loss is neglected. Therefore, the attenuation at the resonant frequency of this filter becomes infinite in the computation and is significantly different from the practical situation. To resolve this problem, the present paper derives theoretical equations including the conductor loss from the equivalent circuits for not only this filter but also the multiple-slit type and the multiple rectangular-plate type which are newly developed for mass production. The theoretical and experimental values are compared. It is confirmed that the frequency characteristics of the attenuation of the filter can be estimated theoretically including the resonant point.