On the Negative Delay Time of a Narrow-Band Signal as It Passes Through the Resonant Filter of Absorption

Abstract

It is shown that a narrow-band signal with smoothly varying envelope can have a negative delay time upon filtering by certain physically realizable filters, i.e., the smooth-signal envelope shifts forward rather than backward. We show that this does not contradict the casuality principle, since the advanced appearance of the signal has the nature of prediction of the future signal level from the time dependence of its level in the past. It is shown that in the case of a negative delay time, the time dependence of a switched-off signal can be recovered, i.e., reception of the untransmitted part of the signal is possible. We propose to use these phenomena for predicting signals of natural and artificial origin.