Features of Reception of Signals with Linear and Circular Polarization in the Incoherent Scatter Technique

Abstract

The features of the use of radio waves with linear and circular polarization at incoherent scatter (IS) radars of the very high frequency (VHF) band are considered. We give examples of calculating the altitude distribution of the ionospheric electron density from the results of measurements calibrated with the ionosonde data when using the circularly polarized sounding signal, as well as from the IS signal power minima and maxima associated with the Faraday rotation when using a linearly polarized signal. The disadvantages of these methods are noted. In the first case, the ionosonde data are bound to the obtained by IS technique normalized altitude profile of the electron density only at one altitude point; at certain events in the ionosphere, the ionosonde data may be unreliable or even absent (for example, in the presence of the sporadic <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{E}_{s}$</tex> layer). In the second case (the mode of analyzing the wavelike altitude profile of the IS signal power), there are errors in determining the centers of the nodal points, especially when signal-to-noise ratio is low. We proposed a version of calculating the absolute values of the electron density using an altitude profile that is the result of multiplying the voltages of two circularly polarized components of the linearly polarized IS signal with opposite directions of the electric field vector rotation, when the linearly polarized sounding signal is used. In this case, a wave-like alternating function associated with the Faraday Effect is obtained with the help of special calculations. This function is used to determine the intervals between its adjacent zero values, and the resulting height intervals are uniquely related to the average electron density for each of them. Due to the high accuracy of determining the points of intersection of the function with the abscissa axis, the accuracy of electron density measurements using the Faraday Effect increases significantly, especially in the presence of noise. We proposed a structure of upgraded hardware for implementation of such mode of additional processing of the IS signal orthogonal components. Using computer simulation, an example of the separate reception of circularly polarized components of the IS signal with their multiplication is given, including a situation when noise-like components are present.