Partial modal degeneracy in lossy magnetron cavities

A type of partial modal degeneracy in cavities, meaning the coincidence of one of its electromagnetic characteristics with varying mode index, is stud ied for TE-modes of unloaded magnetron cavities with Ohmic losses. Based on the analytical predictions obtained by using the principal (zero) spatial harmonic approach (PSHA) and on numerical results obtained in the framework of the standard mode-matching technique (MMT), it is shown that a modal de generacy in the dependence of the imaginary part of the natural frequency o n the aperture opening can occur. The limiting behavior of both dependencie s of the real and imaginary part of the natural frequencies on the aperture opening obtained for the pi -mode is studied in detail. Efficient approxim ate formulae are proposed for the limits of the complex natural frequencies .