We propose a design equation for the resonant frequency of FSS radome due to the dielectric cover effect. The FSS radome structure is composed of the single layer arrays of square loop symmetrically embedded in a dielectric layer. This equation was obtained through the curve fitting method based on FSS radome's fullwave simulation for various thickness and different permittivity. To validate the proposed equation, the FSS radomes having various thicknesses were fabricated and measured for prediction of their performance. From the obtained results, we also present the dielectric thickness range of FSS radome that the proposed equation can be applied. We believe that the proposed equation is very useful to design FSS radome and can be applied to various communication and electrical instruments.