Dispersion distortions of wide spectrum signals during their propagation in the Earth ionosphere

Abstract

The current trend in the development of radio engineering systems (RES) is to use wide spectrum signals, the application of which provides an increase in the resolution and secrecy of the radar operation, an increase in the speed and volume of transmitted information for communication and telemetry systems. The class of such signals includes ultrashort pulses (USP signals), radio pulses with linear frequency modulation (chirp signals). Also of interest are ultra-wideband (UWB) noise signals (UWBN signals), which have high electromagnetic compatibility, stealth and noise immunity. When designing promising ground-based and space-based RES using wide spectrum signals, an important task is to determine the distortions of their envelope shape and distortions of spectrum, as well as the change in the polarization of the emitted wave when passing through the Earth's ionosphere, since taking these distortions into account will provide conditions for optimal reception. This article presents the numerical assessment results of the expected distortions of the wide spectrum signals main types of the decimeter wavelength range, for middle latitudes at heights from 100 km to 1000 km. The conversion of the emitted pulse into a frequency modulated radio pulse is typical for the USP signal. For a chirp radio pulse with a monotonically increasing frequency, an initial decrease in duration with an increase in amplitude and subsequent stretching in time with further spread is typical (the amplitude change is estimated due to a change in the signal shape without taking into account spread). For a chirp radio pulse with a monotonically falling frequency and a UWBN signal, dispersion distortions manifest themselves as an increase in their duration with a decrease in amplitude. For all signal types under consideration that have passed through the ionosphere, a leading edge lag is observed, the dependences of frequency on time at an altitude of 1000 km are repeated and are close to hyperbolic character, the energy spectra envelope shape of the considered signals is almost not distorted. The polarization plane rotation for signals with a spectrum concentrated in the frequency range above 0.7 GHz does not exceed 45