Which of the following best describes the radiation pattern of a quarter-wave ground-plane vertical antenna?
Bi-directional in azimuth
Isotropic
Hemispherical
Omnidirectional in azimuth✓الإجابة الصحيحة
الشرح
The current on a vertical element is symmetric about its axis, so radiation is the same in every compass direction and varies only with elevation angle. Isotropic would mean equal radiation in every direction including straight up, which a vertical does not do because it has a null off its top.