In this work the effect of different elements on the absorption properties of a microwave absorber based on their atomic radii, have been investigated. A theoretical analysis is made using transmission line theory and dielectric theory. Mathematical relations between the refraction index, permittivity, loss tangent and attenuation constant of a microwave absorber are evaluated with respect to the atomic radii of the given element. Atomic radii play an important role in the polarization mechanism of a microwave absorber. Thus a theoretical understanding of the extent of the effect of the atomic radii on the absorption performance can be helpful in selecting suitable elements for various applications of an absorber. The elements with high attenuation constant are tabulated with examples of their respective compounds which have been experimented for microwave absorption performance in various literature. © 2022 IEEE.