VLF Wave Transmission from a Dipole Antenna in Cold Magnetized Plasma

We present theoretical study on very low frequency (VLF) wave radiation from a dipole antenna in a cold magnetized plasma. We have derived antenna impedance and radiation wave electric field based on the Fresnel zone construction theory [Song et al., 2021], considering the case with the antenna oriented in right angle with respect to the ambient magnetic field. In that study it is shown that radiated waves from the antenna with different propagation directions interfere in space. Regions of enhanced waves are formed when the interference is predominantly constructive at the observing point. The coherently enhanced wave propagates at the group velocity. If the antenna is perpendicular to the background magnetic field, the regions of strong waves form two back-to-back Fresnel zones that are parabolic-shaped cones along the background magnetic field from the antenna. The power within each cone drops with distance at a rate of 1/r much more slowly than the decrease of the power of a spherical wave with the distance as in vacuum. In this study we extend the theoretical analysis to the situation that the antenna in arbitrary angles relative to the ambient magnetic field and show the dependence of the antenna reactance on the antenna orientation with respect to the ambient magnetic field.