Reflection of radiowaves from the two-layer isotropic ionosphere in the regions of near-critical frequencies

Using the method of standard equation, a unified analytic expression for the radiowave reflection coefficient from the two-layer ionosphere is derived. The expression is valid for all frequencies. In the region of semitransparency for the E layer, the multimode structure of the reflected signal is studied, and the cause of a substantially nonmonotonic frequency behavior of characteristics of the total response from the ionosphere to a perfectly narrowband sounding radio signal is revealed.