The slotted ring resonator has some promising features for the realisation of compact microwave filters. For the first time, using the finite difference technique and conformal mapping method, the effects of geometrical parameters (i.e.: the resonator length, inner radius, gap width and wall thickness) on the resonant frequency of this resonator, are investigated. The fine tuning of the resonant frequency in practice, is also addressed and in this connection, experimental results are presented.