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Smart structures with tunable electromagnetic characteristics are required for camouflaging high-value targets, such as land warfare moving equipment, in continuously changing complex electromagnetic environments. The targets must control their radar cross section (RCS) to avoid detection and tracking. Frequency selective surfaces (FSSs) are the next-generation smart structures in which active RCS control is realized via impedance loading. In this paper, a multistate transformable FSS absorber/reflector that operates in the 3.9–11.0 GHz band is introduced and analyzed. The reflectivity amplitude of this absorber/reflector could be smoothly changed from 0 to -10 dB in 6.0-8.0 GHz. Each unit cell of the FSS structure consisted of four symmetrical diamond-shaped patterns, and the adjacent units were connected by PIN diodes. The absorption intensity of the FSS could be changed from 0 to -10 dB by adjusting the PIN bias voltage, which was applied via a simple bias network. The multistate switching characteristic of the FSS was verified by simulations and measurements. The results showed that adjustable absorbing intensity and switchable working states are the desirable characteristics that allow high-value targets to adapt to changing electromagnetic environments. Our work will bridge the gap between the available stealth strategies and practical applications, such as moving stealth vehicles.

A multisection step-impedance honeycomb absorbing structure is investigated both theoretically and experimentally. Excellent intrinsic impedance matching and low reflection are realized by providing a step-impedance transition between air and metal in the microwave band. The wideband absorption mechanism of the honeycomb absorbing structure is analyzed using a step-impedance model, and the particle swarm optimization algorithm is used to obtain the optimal step impedance. Two absorbing structures were simulated: The double-layer structure had an absorption frequency band of 3.9–12.4 GHz and a thickness of 9 mm, and the triple-layer structure had an absorption frequency band of 2.2–12.4 GHz and a thickness of 15 mm. The measured reflectivity values were consistent with the calculated results, thereby confirming the validity of our designs for the absorbing structure.