Design of an optically-transparent ultra-broadband microwave absorber

The optical window of low-observable platform needs to be compatible with ultra-broadband absorption, hence an optically-transparent absorber with ultra-broadband absorption is designed and analyzed in this paper. The transparent materials indium-tin-oxide (ITO) film and polymethylmethacrylate (PMMA) are selected as the lossy layer and the supporting dielectric layer, respectively. The optically-transparent ultra-broadband absorber (OT-UBA) is composed of three layers of ITO square patterns, three layers of PMMA dielectric and a uniform ITO plane. The ITO square patterns can realize arbitrary equivalent series of RC (resistor and capacitor) circuit, so that three layers of ITO square patterns together with the ITO plane can achieve ultra-broadband absorption based on the equivalent circuit optimization. Measured results shows that the 90%-absorption bandwidth covers 2-17 GHz while the light transmittance achieves 59.6% with a total thickness of only 12.9 mm.