How does antenna height affect the azimuthal radiation pattern of a horizontal dipole HF antenna at elevation angles higher than about 45 degrees?
If the antenna is too high, the pattern becomes unpredictable
Antenna height has no effect on the pattern
If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional✓الإجابة الصحيحة
If the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated
الشرح
The end nulls of a dipole are nulls only in the plane of the antenna. At high elevation angles, especially for an antenna lower than one-half wavelength where ground reflection dominates, those nulls fill in and the azimuthal pattern becomes nearly circular.