Questions about low-noise amplifiers (LNAs) and their application in receiving antenna systems.

A low-noise amplifier (LNA) is an designed to amplify very weak signals while adding a minimum of noise to the output.

In antenna systems, a LNA may be placed between the antenna and feed line (as opposed to between the receiver and feed line) in order to improve the signal-to-noise ratio found at the receiver after losses in the feed line; this is particularly useful for higher frequencies where losses in transmission lines are significant.

If the same antenna is to be used for transmitting, a transmit/receive switch must be used to bypass the amplifier when transmitting.