Let’s take the example of a single-band UHF antenna. This looks a bit like a fish skeleton. The “bones” are arranged in pairs on opposite sides of a central “spine”. The bones near the front are shorter than those near the back. The critical difference of course is that an antenna is made of metal. The antenna needs to be made of something conductive to receive the electromagnetic wave that we call the TV signal.
When an electromagnetic wave hits the conductor it generates a small voltage. A simple aerial consists of a bar or rod of metal cut in half. A feeder cable is connected across the cut. This simple type of antenna is called a dipole.
If the dipole is half the size of the electromagnetic waves the reception is more efficient. Another way of improving the antenna is to add further rods (the technical phrase is elements) in front of the dipole. Positioned precisely and cut slightly shorter than the dipole they act as “directors” to concentrate the electromagnetic waves on the dipole. Of course they have to be attached to a central “spine” to keep them in place. This bit is called the boom.
To reduce ghosting and interference from transmitters located behind the receive antenna additional elements can be added behind the dipole. They are longer than the dipole and are called reflectors. In the best antennas these aren’t simply single rods but a vertical mesh or array of rods, angled towards the front of the antenna. This type of antenna is called a Yagi, after it’s Japanese inventor.
There are other types of TV antenna. Set-top antennas tend to be simple loops (technically they’re folded dipoles) or rabbit-ears. The latter of course are simple dipoles with the two halves angled towards each other. One type of rooftop antenna you may see is the “bowtie”. This consists of a type of folded dipole in front of a mesh plate. This design isn’t as efficient as a Yagi but does reject interference from the rear pretty well. For this reson it’s a good antenna for use near the transmitting station. It’s possible to mount bowties one above another and connect them together so the outputs electrically add together. This is a good technique where good rear rejection needs to be combined with higher efficiency.
VHF radio and TV antennas are almost always of the Yagi design. The elements are longer and further apart than a UHF Yagi. Sometimes you see dual band antennas with long elements on the same boom as more numerous shorter elements for a higher band.