Propagation characteristics analysis of high-frequency radio waves in the lower ionosphere layers

In this article, the propagation of high-frequency (HF) plane electromagnetic waves through the lower ionosphere is numerically investigated using the real geometry of the Earth's magnetic field in the northern hemisphere. For this purpose, the profiles of electron density and the collision frequency in the layers of the lower ionosphere (D- and E-region) are considered using the reported experimental data for day and night. The reflection, transmission, and absorption coefficients of HF radio waves in the frequency range of 3 to 30 MHz are calculated in the ionosphere plasma. The influences of the collision frequency profile, the magnetic dip angle of Earth's magnetic field, and left- and right-handed polarization on the propagation of HF radio waves have also been investigated. The obtained results indicate that the left-handed polarized wave propagates more easily through the lower ionosphere than the right-handed polarized wave because its transmission coefficient is larger during the day and night. The effect of polarization on the absorption and transmission coefficients is observed for wave frequencies less than 10 MHz at night. It is also demonstrated that the effect of magnetic dip angle on the propagation of left- and right-handed polarized waves exhibits opposite trends in the lower ionosphere. The results show that the propagation of radio waves in the frequency range of 3 to 30 MHz is easier during the night, and the linear decreasing profile of the collision frequency compared to the fixed collision frequency increases the wave transmission in the lower ionosphere.