An Optically Transparent Broadband Microwave Absorber Using Interdigital Capacitance

In this letter, an optically transparent broadband microwave absorber has been developed. The proposed geometry is constructed of the patterned resistive films of an indium-tin-oxide on flexible substrates, such that the structure exhibits broadband absorptivity (above 90%) from 4 to 17.20 GHz (covering C, X, and Ku bands). The novelty of the design lies in leveraging the properties of interdigital capacitance to achieve wide absorption (fractional bandwidth of 124.53%), angular stability, as well as optical transparency compared to the earlier reported broadband absorbers. Moreover, the structure has been extensively investigated through deriving an equivalent circuit model and studying surface current distributions. Experimental validation of the fabricated prototype has also confirmed the potential use of resistive film based broadband absorbers in several applications.