Antenna Feeder System

　　The antenna feeder system is an essential component that connects the antenna to the transmitter or receiver. Its main function is to transfer the electromagnetic energy between the two with minimum loss.

　　Coaxial cables are one of the most commonly used types of feeders. They consist of a central conductor, surrounded by an insulating layer, a metallic shield, and an outer protective sheath. The central conductor carries the signal, while the shield helps to prevent electromagnetic interference from external sources and also acts as a return path for the current. Coaxial cables are popular due to their flexibility and relatively low cost. However, they have some limitations in terms of signal attenuation, especially at high frequencies. The attenuation of a coaxial cable increases with frequency, so for long - distance or high - frequency applications, other types of feeders may be more suitable.

　　Waveguides are another type of feeder system, especially useful at microwave frequencies. A waveguide is a hollow metallic structure, usually rectangular or circular in cross - section. Electromagnetic waves are guided through the waveguide by reflecting off the inner walls. Waveguides have lower attenuation compared to coaxial cables at high frequencies, which makes them ideal for applications where low - loss signal transmission is crucial, such as in satellite communication and radar systems. However, waveguides are more rigid and bulky than coaxial cables, and their installation and maintenance can be more challenging.

　　The impedance matching between the antenna and the feeder is of utmost importance. If the impedance of the antenna and the feeder do not match, a significant portion of the signal will be reflected back, resulting in power losses and reduced antenna performance. To achieve impedance matching, various techniques can be used, such as the use of impedance - matching transformers or stubs. These devices adjust the impedance of the feeder to match that of the antenna, ensuring efficient power transfer.