Journal of Radio Electronics. eISSN 1684-1719. 2025. ¹7

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DOI: https://doi.org/10.30898/1684-1719.2025.7.2

 

 

 

ON THE PROPAGATION VELOCITY OF A NARROW-BAND SIGNAL
IN A DISPERSING MEDIUM
(USING THE METHOD OF MOMENTS)

 

N.S. Bukhman

 

Samara State Technical University,
443100, Russia, Samara, Molodogvardeyskaya str., 244

 

The paper was received March 20, 2025.

 

Abstract. It is shown that the average group velocity over the signal spectrum (both subluminal and superluminal) describes the movement of the «center of gravity» of not all, but a wide class of narrowband signals for any length of the path, including beyond the range of applicability of the first order of the classical theory of dispersion, where the time dependence of the signal is usually significantly distorted. The absorption dispersion inevitably distorts the frequency distribution of the signal spectrum as the length of the path increases, so its group velocity changes accordingly. So, in particular, the initial superluminal group velocity may change to sublight as the length of the route increases. Moreover, for any signals with an unlimited spectrum (including for any signals of artificial origin), with a sufficient length of the route, this is inevitable. The reverse transition from sublight group velocity to superluminal velocity is impossible. It is shown that any signal with a carrier frequency located near the central frequency of the spectral absorption line travels at the initial section of the path with a superluminal group velocity, and its absorption is insignificant. Of course, as the length of the route increases, this superluminal group speed usually changes to sublight.

Key words: wave pulse, group velocity, superluminal group velocity, subluminal group velocity, dispersing medium.

Corresponding author: Bukhman Nikolay Sergeevich, e-mail: nik3142@yandex.ru

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For citation:

Bukhman N.S. On the propagation velocity of a narrow-band signal in a dispersing medium (using the method of moments).  // Journal of Radio Electronics. – 2025. – ¹ 7. https://doi.org/10.30898/1684-1719.2025.7.2 (In Russian).