Field-Strength Variations of LF One-Hop Sky Waves Propagation in the Earth–Ionosphere Waveguide at Short Ranges

One-hop sky-wave signals in the Earth-ionosphere waveguide are studied based on the traditional wave-hop theory and the finite-difference time-domain (FDTD) method. Field-strength variations of 100 kHz one-hop sky waves are given under three different waveguide models. The great-circle distance between the transmitter and the receiver is within 200 km. Together with a sky- and ground-wave separation technique in time domain, the narrowband Loran-C signals are employed in the FDTD method. Compared to the results of wave-hop theory, field-strength variations of low-frequency one-hop sky waves are better characterized by the FDTD method as the waves propagate in an irregular Earth-ionosphere waveguide.