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1. A measure of the rate of attenuation per unit length; the rate of
flux-density (or power) reduction as energy (visual, electromagnetic,
acoustic) propagates from its source. Also called attenuation factor,
decay constant. Compare attenuation coefficient.
For free-space transmission of radar frequency energy, the
attenuation constant is usually expressed in decibels per mile or
kilometer (db/mi or db/km).
2. Specifically, of a traveling plane wave at a given frequency, the
relative rate of decrease of amplitude of a field component (or of
voltage or current) in direction of propagation in nepers per unit
length.
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