Journal of Radio Electronics. eISSN 1684-1719. 2025. ¹5

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DOI: https://doi.org/10.30898/1684-1719.2025.5.15

 

 

 

ON THE RELATIONSHIP BETWEEN SUBLUMINAL
AND SUPERLUMINAL GROUP VELOCITY DURING PROPAGATION
OF AN ELECTROMAGNETIC PULSE IN A DISPERSING MEDIUM

 

N.S. Bukhman

 

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

 

The paper was received February 19, 2025.

 

Abstract. It is shown that there are no dispersing media with «subluminal only» or «superluminal only» real group velocity – if in some medium at some frequencies the real group velocity is subluminal, then in the same medium there are necessarily frequencies at which the real group velocity is superluminal. Conversely, if a medium has frequencies with a superluminal group velocity, then it necessarily has frequencies with a subluminal group velocity. In other words, there is a necessary connection between subluminal and superluminal group velocity – if any medium is capable of generating subluminal group velocity, then the same medium is capable of generating superluminal group velocity. Similarly, there are no media with «only positive» or «only negative» imaginary part of the complex group velocity – if at some frequencies the imaginary part of the group velocity is positive, then at other frequencies in the same medium it is negative and vice versa. This means that if there is a carrier frequency in the medium at which some linearly frequency-modulated signal propagates at a speed lower than the group speed, then in the same medium there is necessarily a carrier frequency at which the same signal will propagate at a speed higher than the group speed and vice versa.

Key words: group velocity, superluminal group velocity, subluminal group velocity, complex group velocity, dispersing medium.

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

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For citation:

Bukhman N.S. On the relationship between subluminal and superluminal group velocity during propagation of an electromagnetic pulse in a dispersing medium. // Journal of Radio Electronic. – 2025. – ¹. 5. https://doi.org/10.30898/1684-1719.2025.5.15