A low profile and wide tunable absorber with varactor in S-band

In the paper, a simple structure is designed to realize a relative wide tunable electromagnetic absorbing in the S-band. The structure consists of rectangle metal patch with slots, FR4-substrate and a varactor. By regulating the DC voltage, the capacitance value of the varactor can change from 1pF to 5pF, resulting the absorbing frequency varying from 3.37GHz to 2.48 GHz, the relative bandwidth can reach up to 30.42%. And at the same time, the absorption rate under these capacitance values of the varactor all can exceed 95%. What's more, the tunable absorber is low-profile with the dimension of unit cell 0.15λ* 0.15λ *0.008λ, where theλ is the free space wavelength at center frequency.