Carbon nanofibers (CNFs) were used as dielectric lossy materials and NiFe particles were used as magnetic lossy materials. Total twelve specimens for the three types such as dielectric, magnetic and mixed radar absorbing materials (RAMs) were fabricated. Their complex permittivities and permeabilities in the range of 2~18 GHz were measured using the transmission line technique. The parametric studies for reflection loss characteristics of each specimen to design the single-layered RAMs were performed. The mixed RAMs generally showed the improved absorbing characteristics with thinner matching thickness. One of the mixed RAMs, MD3 with the thickness of 2.00 mm had the 10 dB absorbing bandwidth of 4.0 GHz in the X-band (8.2~12.4 GHz). It also showed very broad 10 dB absorbing bandwidth as wide as 6.0 GHz in the Ku-band (12.0~18.0 GHz) with the thickness tuning to 1.49 mm. The experimental results for selected several specimens were in very good agreements with simulation ones in terms of the overall reflection loss characteristics and 10 dB absorbing bandwidth.