Phase behavior and dispersion blurring of the signal in the region of the critical frequency of an ionospheric layer

A rigorous expression for the second (frequency) derivative of the reflected monochromatic wave for a parabolic layer is obtained and investigated. It is concluded that there exists a finite, maximum dispersion blurring of a quasimonochromatic signal and that there exists a group lag relative to the critical frequency. Results of calculations for characteristic ionospheric conditions are presented.