Abstract :
It is shown on the basis of quite general assumptions that feedback currents introduced into an antenna structure by means of active amplifying elements cannot lead to an improvement in signal-to-noise ratio over that achievable by using the same antenna structure and amplifiers in a conventional manner. Implications and limitations of the general theorem are discussed. In particular, it does not appear possible to use current feedback of the type considered in a small untuned antenna to obtain the improved SNR which is achievable over a narrow band by means of high-quality loading coils and matching networks.
