Accurate variational analysis for measurement of complex dielectric constant of the sample rod inserted in a cavity

This paper derives the Lindell formula based on the generalized variational principle. For the complex dielectric constant measurement of a small lossy dielectric rod with Rayleigh-Ritz method, an accurate variational analysis is given. The concept of complex frequency {Mathematical expression} is introduced in general, and the stability of the solution is discussed. Comparing with the result of perturbation method, it is concluded that the deviation, of perturbation algorithm should be taken into consideration.