The requirements for antennas designed to operate with a ham radio depend on what bands the operator wishes to access. Height, size and configuration are primary considerations for any antenna designed to work with a ham radio.
Taller and larger antennas generally operate more efficiently, but no antenna radiates energy without some loss. Ham radio operators who want to access lower frequencies need larger antennas. A miniature high frequency antenna is not as efficient as a full size antenna because it loses radio frequency energy as heat. A vertical antenna that is not a dipole must have radial arms in order to allow radio wave currents to return to the antenna; a vertical antenna without radials can still function, but it is less effective.
Antennas designed to work in the ultra-high frequency and very-high frequency bands are similar to other antennas, but they can be smaller and still function efficiently. Directional and omnidirectional antennas are both used by VHF and UHF ham radio operators. An example of a directional antenna is the parabolic dish used for TV reception; this offers maximum distance and minimum interference in transmission. Mobile antennas such as those on vehicles are omnidirectional, and they are commonly used for transmitting and receiving in all directions at once.