Reducing RCS of Patch Antennas via Dispersion Engineering of Metamaterial Absorbers

In this paper, a low radar cross section (RCS) patch antenna is proposed, which is realized by engineering dispersion property of metamaterial absorbers (MAs). The dispersion curve of the MA consists of a weak linear regime with low insertion loss and an asymptotic nonlinear regime with strong absorption. By changing geometric parameters, the dispersion property of the MA can be engineered, so that the cutoff frequency is shifted freely, as well as the strong absorption band being changed. Thus, if the cutoff frequency of the MA is very close to the upper bound frequency of a patch antenna, the patch antenna will obtain polarization-independent low-RCS property out-of-band or in-band cross-polarized and out-of-band copolarized low-RCS properties by replacing the radiation patch with the modulated MA. For verification, a C-band patch antenna with RCS reduction performance in X-band is designed, fabricated, and measured. Both the simulated and measured results agree well and verify that the antenna achieves average gain about 5 dB in 7.2-7.7 GHz. To assess the RCS reduction performance of the proposed patch antenna, we fabricated a 5 x 5 antenna array. The measured results indicate that monostatic RCS of the array is decreased by more than 10 dB in the entire X-band for copolarized and cross-polarized wave normal incidence than the metallic plate with the same area.