Design of thin microwave absorbers using capacitive screen

A microwave absorber with a layer depth less than a quarter wavelength is investigated based on an equivalent circuit. For a specific absorber with a given layer electrical length, the equivalent resistance and capacitance of a capacitive screen can be determined using the presented closed-form design equations. The relation between the layer depth and absorption bandwidth is also analyzed. The presented formulation is validated by a design example in the ISM band. A unit of the absorber screen is realized using a resistive rectangular structure with surrounding gaps. The absorber is shown to offer a 90% absorption bandwidth from 2.3GHz to 5.1GHz (93%) with layer depth of 1/8 wavelength.