Which of the following best describes the radiation pattern of a quarter-wave ground-plane vertical antenna?

A quarter-wave ground-plane vertical antenna radiates radio frequency energy equally in all compass directions. In radio terminology, the horizontal plane around the antenna is called the azimuth. Because the antenna radiates equally in all horizontal directions, its azimuthal pattern is described as 'omnidirectional.' This characteristic makes vertical antennas excellent for general communication where you want to reach stations in any direction without physically turning the antenna. Distractors like 'isotropic' are incorrect because an isotropic radiator is a theoretical point source that radiates equally in a full 3D sphere (including straight up and down), while 'bi-directional' typically describes a horizontal dipole, not a vertical.