Radar signals can penetrate loose sediments such as dust, sand, and alluvium to reveal buried geologic structures obscured in visible and infrared images. In anticipation of data from instruments such as the MARSIS and SHARAD radar sounders and potential future imaging SAR and rover-mounted GPR instruments, measurements have been made to characterize electrical loss factors of a Martian dust analog and an iron-rich soil. This paper presents results from dielectric measurements of Carbondale Red Clay (CRC) and the palagonitic Mars JSC-1 soil simulant from 0.2 to 1.3 GHz and from transmission measurements of radar penetration of CRC up to 12 GHz. Attenuations predicted from dielectric measurements are compared to values measured in the experiment and are discussed relative to the frequencies at which imaging radars operate. Over the frequencies considered, loss tangent, tan δ, decreases with increasing frequency, but attenuation increases due to the influence of wavelength. Attenuation in CRC ranges from 8 to 22 dB/m over P and L bands and jumps to 36 and 67 dB/m at C and X bands, respectively. Mars JSC-1 has lower attenuation of 5 dB/m at P band and ~12 dB/m at L band. Compared to attenuation measurements of sand, both CRC and Mars JSC-1 cause significantly greater attenuation, likely due to their compositions containing iron-bearing minerals. Because Martian fine sediments also contain ferric mineral components, constraining higher losses of analogs for Martian dust and fine sediments is important for predicting the performance of radar instruments operating in orbit or on the surface of Mars.