Design of wideband absorbers using simple closedform solutions

Simple closed-form design equations (or solutions) for microwave absorbers with high absorption and wide bandwidth are derived based on an equivalent circuit. One interesting fact about the solution is that the zero slope (of the reactance or the susceptance) condition has been used. For an absorber with a certain center frequency, the equivalent circuit values are determined using the presented design equations. The required circuit values are shown to be realized by a 2D periodic surface of which unit is composed of a resistive cross-shaped structure, a conducting plane, and a spacer between them. The presented formulation is validated by a design example for an absorber used at X-band. Based on 90% absorption, the bandwidth is 4.7 GHz (7.8 GHz - 12.5 GHz) with 100% absorption at the center frequency of 10 GHz. The absorber is also shown to be insensitive to polarizations of incident waves.