Beam defocusing in crts with traveling-wave deflection plates

At high frequencies, traveling wave vertical deflection structures for crts have electric field components in all three axes. Ez, the component aligned with the length of the deflector, causes velocity modulation of the electron beam. This results in trace widening of the displayed signal. Differences in transit time for electrons traveling between the vertical and horizontal deflectors result in trace widening that is uniform across the screen. At the same time, velocity sorting in the horizontal deflector produces trace widening proportional to distance from the center of the screen. It is necessary for engineers to take these effects into account when designing crts for use above one gigahertz.