If a quarter-wavelength vertical antenna is placed on the roof of a car, in what direction does it send out radio energy?

A vertical antenna installed on a uniform, flat surface, such as the center of a car roof, operates as an omnidirectional antenna. This means it radiates radio frequency energy uniformly in a 360-degree circle along the horizontal plane. The large metal roof of the car serves as a highly effective ground plane. This uniform metal surface helps the antenna radiate efficiently and equally in all horizontal directions without heavily favoring the front, back, or sides of the vehicle. A vertical antenna does not radiate most of its energy straight up (unlike an NVIS antenna setup), nor is it highly directional like a Yagi. While placing the antenna on a corner bumper might skew the pattern, a center roof mount ensures a balanced, omnidirectional signal.