Input circuits when working with tuned antennas. General information

Tuned antennas are usually used when receiving at ultra-high frequencies, at which the dimensions of the antenna are comparable to the long wavelength. In addition, such antennas are used for professional reception and at lower frequencies. In these cases, there are high demands on the sensitivity of the receiver, which is limited by the receiver's own noise. Therefore, it is important to ensure the best signal power transfer from the antenna to the input of the first active element of the receiver. Maximum power transfer will be when matching the antenna with the feeder, and the feeder with the input of the receiver. In this case, the feeder will have a traveling wave mode, which is also necessary to eliminate signal distortions caused by reflections at a long feeder length.

When the receiver operates with a tuned antenna, the latter is represented as an EMF source. possessing only active resistance . The antenna introduces active conductivity into the input circuit, which entails an expansion of the bandwidth. When working with a tuned antenna, power matching, optimal matching, or noise matching are relatively simple. The corresponding mode is usually implemented at the center frequency of each subband or at each fixed frequency.

The mode of operation with a tuned antenna circuit can be implemented by using a special body of tuning the antenna circuit. This mode is also carried out when the receiver operates at one frequency or in a very narrow frequency range, when the geometrical dimensions of the antenna can be chosen so that at this frequency the antenna has a pure resistance.

When working with a tuned antenna circuit, input devices with transformer and auto-transformer coupling are practically used.