A radar sounder for the study of the refractive index structure in the troposphere is described. The specially built, high-sensitivity FM-CW radar has a maximum range resolution of one meter. Design considerations and performance characteristics are given, and recordings obtained with the radar sounder are presented and discussed. The predominant layers are very well correlated with the major inversions at which we find either sharp vertical gradients of refractive index or changes in the gradient. The base of the lowest inversion is almost always so marked. A second echo layer frequently appears some tens of meters above this base level.Although the echo strata may sometimes be 30 to 40 meters in depth, they are often only a meter or less thick. Their reflectivities may be 10 to 100 times larger than those previously reported with radars of coarser resolution. The layers also commonly appear in the form of breaking Kelvin-Helmholtz waves with periods of 2 to 4 minutes and peak-to-peak amplitudes as small as 10 to 15 meters.