The dielectric function of the ionosphere is () / 0 = 1 2 /

The dielectric function of the ionosphere is ε(ω)ε / ε₀ = 1 − Ω²/ω², where is a constant. Explain why a radio operator, exploiting the reflection of radio waves from the ionosphere, nearly always receives signals with ω > Ωfrom distant broadcasting stations, but only occasionally or never receives signals withω > Ωfrom nearby stations.