An analog frequency resolved electrical gating (FREG) system based on a composite right/left-handed (CRLH) leaky-wave antennas for UWB signal characterization is proposed. This system is based on spatial-spectral decomposition property of the leaky-wave antenna and on the self-gating principle to suppress the time-frequency resolution dependence on the antenna physical length in the spectrograms. The system is demonstrated numerically using an efficient time-domain Green's function technique and spectrograms are shown for various time domain test signals.