We report on experiments carried out on a backward transmission line, which consists of a fin-line periodically loaded by split-ring resonators and shunt wires. We first demonstrate the left-handed character of these frequency-selective transmission lines via: 1) dispersion diagram calculations which have been compared to the frequency dependence of measured scattering parameters; 2) the tracking of the phase fronts; and 3) the phase offset between two lines of various lengths. The effective refraction index found experimentally was approximately -4. Taking benefit of the use of a closed electromagnetic system and successful matching, the losses are especially analyzed. The ratio between incident and absorbed energy is 65% for a three-cell prototype and reaches 91% for ten cells.