Effect of Induced Electromotive Force on a VLF Linear Antenna in an Anisotropic Plasma

In this article, the effect of an induced electromotive force (EMF) on the electrical characteristics of a linear antenna in an anisotropic ionosphere over a very low-frequency (VLF: 3-30 kHz) range is investigated. By establishing a technically sound mathematical model of a linear antenna with a motional status relative to the geomagnetic field, the induced EMF effect on the current distribution and input impedance of a linear antenna is first systematically analyzed and quantified. A 3-D kernel function is obtained to match the EMF generated on an arbitrarily oriented antenna. Computations show that as the dip and azimuth angles of an antenna vary in a wide range, the fluctuations on the input impedance always remain within 10%, with the change mainly reflected on the real part. The discrepancy caused by an induced EMF will be more significant when the antenna length reaches 1 km, which should not be ignored for long antennas. This analysis aims to mitigate the undesired effects led by an induced EMF and may provide heuristic support for practical schemes of VLF space-borne applications.