Broadband low-RCS metamaterial absorber based on electromagnetic resonance separation

We have designed and fabricated a broadband low radar cross section (RCS) metamaterial absorber with polarization-independent characteristic based on electromagnetic resonance. The absorbing mechanism is investigated by means of electric as well as magnetic field distributions and retrieval algorithm. Absorbing and RCS properties of this absorber are performed by waveguide experiment and free space measurements, respectively. Theoretical analysis indicates that the absorber can produce electric and magnetic resonances in different locations for fixed frequency, while for different frequencies, it can provide energy losses in different dielectric layers, which effectively lowers the electromagnetic couplings and consequently keep the strong absorbing properties in a wide frequency range. Experimental results show that the designed absorber with 3-layer structure achieves a frequency range which is 4.25 times as that of 1-layer absorber with absorptivity above 90%, its relative bandwidth for RCS reduction above 10dB is 5.1%. The cell size and thickness of the designed absorber are very small, i.e., 0.17 and 0.015 of the working wavelength. Thus the low-RCS property of the absorber is wide-angle and polarization-independent. In addition, the working frequency range of the absorber can be adjusted by properly designing the layers.