Broadband and wide-angle microwave absorption with resistive films printed on a flexible polyethylene terephthalate substrate

A low-cost ultra-thin design (<; 5% λ₀) of microwave absorbing material is presented for easy implementation by printed electronics techniques. It consists of a resistive ground plane coated on one side of a flexible polyethylene terephthalate (PET) sheet and printed on the other side a perforated resistive film, respectively with thicknesses of 100 μm, 250 μm and 100 μm. A square lattice of holes is used for the perforation which allows the absorber´s partial transparency for visible light. With a conductivity of 80 S/m for the resistive films on both sides of the PET substrate, the design gives microwave absorption of more than 50% from 20 GHz to 56 GHz. The good absorption is valid over a wide range of incidence angles, in particular up to 70 ° for a narrow frequency band from 25 to 30 GHz.