A theorem concerning the effect of feedback currents in antenna structures on signal-to-noise ratio

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.