Low-Profile Broadband Absorbers Based on Capacitive Surfaces

Low-profile and broadband absorbers based on capacitive surfaces are proposed and implemented. First, the impedance of a dielectric substrate and capacitive surface is analyzed separately to characterize the surface impedance. The capacitive surfaces are therefore achieved with the combination of two ring resonators and used to design a three-fold and four-fold symmetric absorber. The resulting absorbers, with the thickness of about 0.076 lambda(L) at the lowest operating frequency, exhibit good absorption at -10 dB return loss over the fractional bandwidth of 82.5%-117.4%. For demonstration, one prototype of the proposed absorber was fabricated and measured, and good agreement is observed.