Abstract: In this paper a short cavity resonator which reduces the resonance linewidth of Rb maser is proposed.By using a H₀₃₁ mode cavity and a discal quartz bulb coated with paraffin, the geometric dimension of the cavity was designed, the filling factor of the cavity and the maser oscillating condition were evaluated, and its linewidth is given as compared with H₀₂₁ mode cavity.

Key words: cavity, Rb maser, linewidth