A Step-by-Step Design Methodology for Broadband Tunable Microwave Metasurface Absorbers Using Theory of Characteristic Modes

In this paper, a characteristic mode (CM)-based design methodology is developed for the reconfigurable microwave metasurface absorbers (MMA) with using commercially available substrates. Theoretical intrinsic connection between modal behaviors and absorption properties is first formulated for the design of the structures. As a proof of the method, a broadband MMA consisting of butterfly elements is step-by-step designed. The positions and values of the impedance loading are determined based on the modal significances and modal currents for broadband operation. The absorption performance is evaluated by the formulated theoretical model and verified by full-wave simulation. After that, a flexible implementation a employed for free-form surfaces conformal. Experimentally, the proposed MMA is fabricated and measured. The absorption fractional bandwidth with reflectivity less than -10 dB is achieved from 3.6 to 11.6 GHz (105%). Good agreements between the simulation and measurement results for both planar and cylindrical cases validate the developed CM-based design methodology. The mimicry of time-varying scattering cross section (SCS) is then further realized through real-time coding absorption states, which is a promising candidate for practical electromagnetic systems.