VLF Current Distribution and Input Impedance of an Arbitrarily Oriented Linear Antenna in a Cold Plasma

In this paper, we proposed a semianalytical method for calculating the current distribution and input impedance of a very low frequency (VLF: 3-30 kHz) linear antenna of arbitrary orientation in a homogeneous anisotropic cold plasma. By considering the effect of the geomagnetic inclination angle, the kernel function, in this case, has a more complicated form and requires extra analytical techniques to deal with. The computations show that the amplitude coefficients for the ordinary wave are evidently greater than those for the extraordinary wave. We also found that the shape of the current distribution is not sensitive to the orientation of the antenna, but the total current moment on the antenna will be decreased when the inclination angle becomes larger. Moreover, due to the higher attenuation rates for both the ordinary and extraordinary waves at a propagation direction perpendicular to the magnetic field, the overall trend for the input impedance of the antenna is increasing with the geomagnetic inclination angle. It is then concluded that the optimal posture for a VLF space-borne linear antenna should be as parallel as possible to the direction of the geomagnetic field in order to achieve maximum antenna efficiency.