Assesment of coaxial filters for the instalation of metallic mode stirrers or turntables in multimode microwave ovens

In this contribution authors show the usage of several coaxial filters that avoid microwave leakage when using metallic mode stirrers within microwave multimode cavities. We describe the simulation schemes and characteristics for the different coaxial filters employed when introducing the metal axis of the mode-stirrer in the applicator. Additionally, the measurement setup that allows to validate the filtering capabilities is also described in detail. Figure 1 shows the cross-section scheme of a typical multimode microwave cavity. A waveguide feeding port is used to introduce the microwave energy in the cavity. The movement of the mode stirrer causes different electric field distribution patterns within the cavity and the material which may result in the reduction of cold and hot spots. Metallic materials are preferred versus dielectric ones to manufacture stirrers because metals are more effective than dielectrics to reflect and stir the microwave energy. However, when the metallic axis of the mode stirrer goes through the cavity walls a coaxial line is generated and the microwave electric field may leak through the coaxial port very easily. Several coaxial filtering structures are evaluated and validated to prevent electric field scaping from the applicator.