We have undertaken a laboratory electromagnetic characterization of minerals identified by the Mars Global Surveyor's Thermal Emission Spectrometer (TES) to determine their dielectric properties over the frequency range from 1 kHz to 500 MHz. The study includes the same sample library used for the calibration of TES, volcanic rocks from potential terrestrial analogues sites, as well as some achondrite and SNC meteorite samples. Samples have been measured in two forms: powder and compacted pellets, reflecting the different extremes in soil density and lithology that are found on the Martian surface (the in-situ density of these materials has been estimated from the TES thermal inertia data). The primary objective of this work is to evaluate the range of the surface electrical and magnetic losses that may be encountered by radar sounding investigations that are conducted to identify the state and distribution of subsurface water on Mars. The electromagnetic properties of these Mars-like materials are being investigates as a function of various geophysical parameters, such as porosity, bulk density and grain size. This information will help to locate regions on Mars were surface dielectric conditions are optimal for orbital subsurface sounding. Preliminary results indicate that for low-density dust, the dielectric contrast between different iron-poor minerals is not very relevant while for consolidated materials with equal densities the contrast is more important. In contrast, iron-rich minerals, such as hematite and magnetite, have both a complex dielectric behavior and yield a strong contrast with other minerals detected on the surface of Mars. Even in minor amounts, iron oxides can have a strong impact on the strength of the backscattered radar signal in the frequency band 1 to 30 MHz. We discuss the potential implications of these findings on the maximum penetration depth and effect of surface clutter at the frequencies utilized by the MARSIS and SHARAD orbital radar sounding instruments.