Abstract
As the U.S. and Europe launched the very low frequency (VLF: 3-30 kHz) space-borne transmitting and propagation experiments during the past thirty years, space-borne antennas have been playing a more and more important role in contemporary VLF communication systems, which are very likely to become an indispensable approach for overwater/underwater communication and navigation in the future. In this paper, we propose a semianalytical method for evaluating the current distribution and input impedance of a VLF space-borne tubular antenna. By considering the effects of both the ordinary wave (O-wave) and the extraordinary wave (E-wave) in an anisotropic ionosphere, the analytical expression for the current distribution has a more complicated form and is derived via the method of moments (MoM) and the Gauss-Legendre quadrature (GLQ) algorithm. Computations show that the current distribution and input impedance under anisotropic conditions are very sensitive to parameter changes, but the overall trend for the input impedance will increase with the radius or electrical length of the antenna. Comparisons with linear models and numerical results obtained in FEKO verify the accuracy of this method. From simulations about the effect of the geomagnetic inclination angle to the input impedance, we advise that the parallel case can be preferred as an alternative for the best angle. Once all antenna parameters are determined, there is a possibility to find multiple optimal inclination angles. In addition, qualitative analyses of the impact of environmental changes to the antenna characteristics are also discussed.
Highlights
It is known that the very low frequency (VLF: 3–30 kHz) electromagnetic waves are widely used in overwater/underwater communication and navigation
In this paper, we treat the problem of a VLF tubular antenna in an anisotropic cold plasma both analytically and numerically, and propose a theoretical method for computing the current distribution and input impedance of the antenna
The kernel function of the antenna is obtained by evaluating the near-field, and the six amplitude coefficients in the current equation are determined through the MoM as well as the Gauss-Legendre quadrature (GLQ) algorithm
Summary
It is known that the very low frequency (VLF: 3–30 kHz) electromagnetic waves are widely used in overwater/underwater communication and navigation. He et al.: Current Distribution and Input Impedance of a VLF Tubular Antenna in a Cold Plasma electromagnetic interaction between the TSS and the ambient space plasma [8]. In 1993, the wave propagation theory for a VLF space-borne linear antenna was initially investigated by Bannister et al [6], where the effect of the earth’s magnetic field was only considered on the wave number. In two recent papers by He et al [21], [22], the current distribution and input impedance of a VLF space-borne linear antenna parallel or at arbitrary orientations to the earth’s magnetic field were investigated in detail. We will attempt to propose a new theoretical method for evaluating the current distribution and input impedance of a VLF space-borne tubular antenna. By combining (18) and (20), the boundary condition satisfied by the antenna should be
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