Design of wideband absorbers using RLC screen

Design equations for wideband single-layer absorbers based on the condition of zero slope reactance (or susceptance) at a specific centre frequency are presented. Using the design equations, a microwave absorber is realised employing a cross-shaped strip structure as a unit on an FR-4 substrate with a relative permittivity of 4.6 and height of 3.2 mm. At a design centre frequency of 10.93 GHz, the size of each unit is 9.6 × 9.6 × 3.2 mm and the overall size of the fabricated absorber is 336 × 336 × 3.2 mm. The EM-simulated and measured absorptions are close to 100% at the design centre frequency and their 90% bandwidths are about 47% (the limit for the case of the layer with ε_r = 4.6). The absorption characteristics of the proposed absorber are shown to be almost unaffected by the polarisation angles of normally incident TEM waves.