Abstract: A vertical deflection system for a CRT is disclosed which has a pair of traveling wave deflectors disposed opposite each other across a path of beam from gun to target. Each deflector has a helical conductor in the for of a strip of sheet metal coiled around an elongate core of insulating material. For the provision of a CRT capable of handling a wide band of frequencies, the dispersion characteristic of each traveling wave conductor is optimized through adjustment of the specific dielectric constant of the insulating core. Preferred values of the specific dielectric constant are specified in relation to the characteristic impedance of the traveling wave conductor.