Current Distribution and Input Impedance of an Insulated Linear Antenna in an Anisotropic Plasma

In this article, a new analytical method is proposed to solve the current distribution and input impedance of an insulated linear antenna in a homogeneous anisotropic ionosphere over a very low-frequency (VLF: 3-30 kHz) range. Due to the presence of the insulating layer, both the boundary conditions and the kernel function of the antenna are more complicated. The determination of the wave number k(L) requires extra analytical techniques, as the pole equation satisfied by k(L) will include both the ordinary and extraordinary waves. Computations show that for insulating layers of small thickness, the amplitude coefficient increases with the plasma density. However, if the insulation is sufficiently thick, then the coefficient will only be slightly affected by the plasma parameters. It is, thus, inferred that an insulating layer tends to make the antenna characteristics less dependent on the ambient plasma and, thus, more predictable. In addition, it is found that the input impedance of the antenna significantly increases with the insulation thickness. Calculations of driving-point admittances are presented for two case studies and compared with existing analytical work and the simulation results. Finally, this article may provide some heuristic support for designing VLF space-borne insulated linear antennas.