Abstract: To improve the radiation and scattering performance of waveguide slot antenna, a square loop perfect ab sorbing metamaterial(SLPAM) whose thickness is only 0. 0057 but with maximum absorption of 99. 9% is designed. A waveguide slot antenna with SLPAM is proposed. Simulated and measured results demonstrate that compared with the conven tional antenna, the directivity of the novel antenna with perfect absorbing metamaterial is enhanced remarkably, simultane ously, its in band radar cross section(RCS) is reduced efficiently, and the largest reduction is up to 15. 7dB.