There are many types of amateur radio antennas because licensed ham radio operators (Hams) have many bands and many thousands of possible frequencies they can use for two way radio communication.
Most Hams today pass a simple examination which allows them to start in the hobby with a VHF portable radio which works in the two meter band. These 2m transceivers transmit at around 146 MHz, so a small antenna works well for them.
Other amateur radio operators enjoy the excitement of long range radio, talking over the shortwaves to other hams around town, in other cities or in other countries. They need an amateur radio antenna that is much larger, because the radio signals there vibrate at a lower (and longer) frequency. And a transmitting antenna always needs to resonate (or match) the frequency of the signal it is sending.
So ham radio antennas for the shortwave bands vary from wire aerials that are more than 200 feet long to maybe 66 feet or so. And vertical antennas or towers can go up forty feet or more straight up in the air. All these different two way radio aerials have different strengths and weaknesses in store.
Certain amateur radio antennas are excellent for long range work, others for short range or for mobile or portable use. Then there are beam antennas, which concentrate their power in one direction and suppress signals at their back and sides. These beam antennas need to be mounted on a mast or a tower so they can be rotated and aimed in whatever direction is needed that day.
There are three main designs for beam antennas. These are yagi antennas, quad antennas and broadband log-periodic dipole antennas. Yagi antennas may be single band or multi-band designs, and can he HF, VHF or UHF. The 14 MHz (20m band) is usually the lowest ham band they cover, especially in 3 or 4 band yagi antenna designs. Quad antennas on the HF bands usually have just two elements and can be multi-banded. There are cubical quads and spider quad designs. (On the vhf bands, a quad antenna smaller than HF, so it might have four elements. But yagis are more common for vhf and uhf bands.) On the HF bands, log-periodic antennas are really large – so they are more common with government embassies and the military. Few hams have the money or the real estate for such large shortwave antennas.
The simplest form of amateur radio antenna is the wire half-wave dipole. This is fed in the middle with coaxial cable that runs back to your radio transceiver. If a wire antenna is fed in the middle with twinlead instead of coax, it is known as a doublet antenna. A doublet can be fed with home-made 600-ohm spaced wires, commercially-made 450 Ohm ladder-line or common 300 Ohm TV twinlead. Feed this into a good antenna tuning unit, and you have an antenna which can be used to work on several different ham bands…a simple multi-band ham antenna.
In the early days of amateur radio, many hams hand-built a lot of their radio equipment including the receivers, transmitters and always their antennas. Today its a lot easier to go into a radio store and buy your radio transceiver (two way radio) and a range of amateur radio antennas from different manufacturers.