The object of this study is to design the Radar Absorbing Structures (RAS) having sandwich structures in the X-band () frequencies. Glass fabric/epoxy composites containing conductive carbon blacks and carbon fabric/epoxy composites were used for the face sheets. Polyurethane(PU) foams containing multi-walled carbon nanotube (MWNT) were used for the core. Their permittivities in the X-band were measured using the transmission line technique. The reflection loss characteristics for multi-layered sandwich structures were calculated using the theory of transmission and reflection in a multi-layered medium. Three kinds of specimens were fabricated and their reflection losses in the X-band were measured using the free space technique. Experimental results were in good agreements with simulated ones in 10dB absorbing bandwidth. 㨊吀 Ѐ㘹〻Ⰰ䉵楬摩湧Ⱐ捯湳瑲畣瑩潮湤楶楬湧楮敥物湧