The concept of quality factor enhancement in a two dimensional rectangular dielectric resonator (RDR), based on the phenomenon of edge diffraction suppression by a plasma, is presented. This phenomenon occurs when the plasma exhibits the specific negative permittivity, which makes the RDR separable, i.e., analytically solvable by means of the separation of variables. The Rotman plasma, constituted of metal thin wires is proposed as a practical implementation of this ideal plasma, and the diffraction suppression concept is demonstrated with this plasma by an SIE/MoM approach verified by using a finite element method solver, HFSS. It is shown that a relatively small number of wires (4 times 4) in the plasma is sufficient to mimic a close-to-ideal plasma medium, which suggests a potential for practical applications. This study reveals that the utilization of this plasma allows a strong (high-Q) resonance even for low-permittivity dielectrics otherwise improper to act as resonators.