Nonlinear evolution of a pulse with a linear frequency modulation in a graded-index waveguide

Abstract

[1]  A weakly nonlinear process of propagation of an electromagnetic pulse with a linear modulation of the carrier frequency in a waveguide structure characterized by different scales of inhomogeneity in the transverse and longitudinal directions is considered. Waveguide channels with such properties are formed, in particular, in the ionospheric F layer due to its stratification under the action of powerful modifying pulses. Thus the method proposed is applicable to a description of the processes of radio wave propagation in the ionosphere with local irregularities. The method also may be used for controlling the parameters (duration, amplitude, etc.) of powerful chirped pulses. Chirps are classified in accordance with the ratio between pulse duration and modulation depth. It is shown that the pulse evolution is determined by three timescales, and analytical relations for chirp parameters are established depending on the transverse and longitudinal inhomogeneity.

Received 15 March 2005; revised 27 September 2005; accepted 8 October 2005; published 25 November 2005.

Keywords: Radiowave propagation; pulse evolution; waveguide.

Index Terms: 6984 Radio Science: Waves in plasma; 2487 Ionosphere: Wave propagation; 2439 Ionosphere: Ionospheric irregularities.