Low-noise amplifier
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The low noise amplifier (LNA) is a special type of electronic amplifier or amplifier used in communication systems to amplify very weak signals captured by an antenna. It is often located very close to the antenna. If the LNA is located close to the antenna, then losses in the feedline become less critical. This "active antenna" arrangement is frequently used in microwave systems like GPS, because coaxial cable feedline is very lossy at microwave frequencies.
It is a key component, which is placed at the front-end of a radio receiver circuit. As we know from the Friis' formula that the overall noise figure of the receiver front-end is dominated by the first few stages.
Using a LNA, the noise of all the subsequent stages is reduced by the gain of the LNA and the noise of the LNA is injected directly into the received signal . Thus, it is necessary for a LNA to boost the desired signal power while adding as little noise and distortion as possible so that the retrieval of this signal is possible in the later stages in the system.
