Nonrelativistic particles radiate like dipoles, i.e. the pattern has a null along the direction of motion and a doughnut wrapped round it. Relativistic particles do the same in their co-moving frame, but in the lab frame, the radiation is concentrated near the direction of motion. It's an effect of Lorentz transformation.
However, there's still a null in the actual direction of motion.
Cheers
Phil Hobbs