One varactor-tunable High Impedance Surface (HIS) is proposed and used in design of an active metamaterial absorber. The proposed HIS structure is based on mushroom-type HIS, in which varactors are introduced to adjust the effective capacitance and tune the resonance frequency. The primary ground plane is etched as the bias network for these loaded varactors, and another ultra-thin grounded sheet is attached to the bottom. In addition, the absorbing characteristics are introduced for dielectric loss to construct an active metamaterial absorber. Numerical simulations show that a wide tuning range can be achieved by adjusting the varactor capacitance, and effective absorption is realized at different states. Two identical absorbers, which are loaded with fixed-value chap capacitors of different capacitances, are fabricated and measured using a waveguide measurement setup. Excellent agreement between the simulated and measured results is demonstrated.
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