A television antenna is designed for receiving wireless broadcast television signals. It can classified based on the
- Frequency and size
- Directivity
- Physical Construction
- Application
Frequency and Size
Antennas of television used for High Frequency differ from the ones used for Very High Frequency. The wavelengths of these are different at different frequencies. They even differ in size to spread out signals at the correct wavelength. They are transmitted at the frequency from 41 to 250MHz in the Very High Frequency (VHF), and 470 to 960 MHz in the Ultra High Frequency (UHF) in various countries. They’re manufactured based on the indoor type and outdoor type. In the indoor, they’re present on the top or beside the television. Whereas outdoor have antennas present on the top of the house.
Directivity
Antennas can be either Omni-directional, sectorial or directive. The antennas which are Omni-directional radiate in the same pattern in 360 degrees and the most common types are the Dipole-Type and the Ground Plane.
The Sectorial antennas unlike omni-directional radiate only in a specific area. It can be as broad as 180 degrees, or as narrow as 60 degrees. Directive antennas beam width is narrower even than the sectorial antennas. There are used for long distance links and its types are the Yagi, the biquad, the horn, the helicoidal, etc. Usually the best antennas are those which are highly directive as they can easily discard signals from other sides. The directivity can be determined through the front-to-back ratio which is measured in decibels.
Physical Construction
The construction of the Antennas can be done in many different ways. It can range from simple wires to parabolic dishes, up to coffee cans. Based on the design, they are again divided into 4.
Wire antennas— these are regularly employed in lower frequency.
Aperture antennas— these are utilised in microwave frequency.
Printed Planar Antennas— these are used in microwave frequency.
Reflector antennas—these are used for operating at microwave frequency.
Application
Based on the application, the antennas are categorised into two. They’re Base Station and Point-to-point. Depending on the purpose, different antenna types are used. Base Stations are used for multipoint access, whereas Point-to-Point case is used for connecting two single locations together.
Non- directional or omni-directional antennas are fundamental dipoles or monopoles. Whereas; the complex, directional antennas consists of compilation of elements like dipoles, or make use of one active and numerous passive elements, like in the Yagi antenna.