Three kinds of compact thin subwavelength cavity resonators containing left-handed media: rectangular, cylindrical, spherical

In the present paper we investigate the restriction conditions for three kinds of cavity resonators ({\it i.e.}, the rectangular, cylindrical, spherical resonators). It is shown that the layer of materials with negative optical refractive indices can act as a phase compensator/conjugator, and thus by combining such a layer with another layer made of the regular medium one can obtain a so-called compact thin subwavelength cavity resonator.