Scattering characteristics of metal circular wire gratings in microwave and terahertz ranges

This paper presents the results of numerical analysis by the finite element method of metal circular wire gratings illuminated by plane electromagnetic waves with s-polarization at the microwave and terahertz frequencies. Numerical data made it possible to obtain a closed-form expression for an approximate calculation of the s-transmittance of such gratings in wide ranges of variations in their sizes. The validity and accuracy of this design equation have been tested analytically, numerically, and experimentally. A comparison of the electromagnetic properties of metal gratings with circular and rectangular wires shows some similarity in the behavior of the transmission spectra of both types of gratings depending on the sizes. An extra analytical expression was obtained for circular gratings with a high filling factor. The fabricated prototype of a metal grating with a period of 40 μm demonstrated an extinction ratio of about 120. The results of this study help to better understand the propagation and scattering of EM waves in such 1-D periodic structures at frequencies from 75 to 350 GHz.