Abstract: In this paper, a universal variational equation for solving electromagnetic boundary problems is deduced from Maxwell's equations. It has the advantage that the trial functions are not restricted by the boundary condition. So it is especially useful in solving problems of anisotropio medium of irregular geometry. The resonant characteristics of plasma-filled cavities are analysed by using the Rayleigh-Ritz method. The numerical results in the case of rectangular cavity are in agreement with those from reference^[3]. Besides, the resonant frequencies and Q values of quasi-TEm and quasi-TM₀₁₁ modes are calculated as the functions of plasma parameters, which are of value in the industrial applications of plasmas.

Key words: variational principle, anisotropio medium, plasma, resonant cavity, Rayleigh-Ritz method