Effective methods for suppression of undesired cavity modes using microwave absorbers

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Abstract
To obtain a method for suppressing undesired modes in a microwave cavity in which a higher‐order mode is desired, the relationship between the location of the absorbers and the suppression effect is evaluated theoretically and experimentally for various suppression methods using microwave absorbers. The suppression methods studied are as follows:(A1) A magnetic absorbing material is placed on the bottom of the cavity in the direction orthogonal to the magnetic field of the desired mode; (A2) the material is placed along the null line of the magnetic field of the desired mode; (B1) a conducting absorber is placed along the null line of the electric field of the desired mode; (B2) the conducting absorber is placed in parallel to the surface current of the desired mode on the bottom of the cavity; (B3) the same is placed along the null line of the surface current.By means of the experiment on the power loss of the absorber for the undesired modes, the suppression methods A1and B1are found effective. Useful results are obtained for the design of the absorber. The experimental results agree qualitatively with the approximate analysis results based on the electromagnetic field in the cavity. The power loss of the desired mode due to the deviation of the location of the absorber is discussed. Further, an experiment is carried out for power combining in the cavity with many active devices, which confirms that the loss of the desired mode is smaller in the method B1than in A1.

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