An ultra-broadband coplanar stripline employing a durable 1.4 μm-thick membrane substrate has been devised, fabricated, and tested. Nearly distortionless propagation of terahertz-bandwidth electrical pulses over lengths in excess of 4 mm has been experimentally demonstrated using subpicosecond test signals and a sampling measurement technique based on ultrashort-duration laser pulses. A comparison to pulse propagation data on identical coplanar strips on a GaAs substrate illustrates a dramatic improvement in the radiation attenuation and phase velocity dispersion for the membrane CPS with increasing frequency.