In this paper, we address the problem of capturing the electrical properties of a lossy dielectric slab through reflection coefficient measurements. Different from the previous works, the problem is set as a minimization problem over multifrequency-monostatic/monoview frequency domain measurements. The cost function takes conductivity, dielectric permittivity and thickness of the slab as its variables and measures the squared distance between measured reflection coefficients and analytic formulas. This cost function is minimized via Newton's method. Results show the stability and accuracy of the proposed scheme.