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Since the orientation of a very low frequency (VLF: 3–30 kHz) space-borne antenna relative to the geomagnetic field will change with the satellite orbiting around the earth, precisely computing the near-field excited by an arbitrarily oriented radiator in the ionosphere is of great importance to the antenna analysis in realistic VLF space-borne applications. In this paper, we propose a semi-analytical method for evaluating the near-field of a VLF electric dipole of arbitrary orientation in a magnetized plasma, where the arbitrarily oriented dipole is modeled as the superposition of dipoles parallel and perpendicular to the magnetic field. The near-field in this case consists of the contributions of both the ordinary wave (O-wave) and the extraordinary wave (E-wave). Due to its large attenuation rate, the integral for the O-wave can be directly estimated through numerical integration, while the integral for the E-wave is evaluated with the help of speed-up convergence algorithm and the complex variable theory. Computations show that the O-wave still has comparable amplitudes with the E-wave in the near zone, and the field generated by the dipole perpendicular to the magnetic field is of dominant effects. Moreover, it is found that there exists remarkable “aggregation effect” in the radiation pattern of the E-wave, indicating that the propagable mode in the magnetized plasma propagates mainly along the direction of the magnetic field.

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.

In this paper, the current distribution and an input impedance of a horizontal linear antenna in the presence of a layered region are investigated both analytically and numerically. In particular, we demonstrate the case of a four-layered region. The wave-number and characteristic impedance of an eccentrically insulated antenna are obtained first. Subsequently, the analytical formula for the current distribution on the antenna in a four-layered region is derived by applying a limiting process. The computational results show that the upper and lower dielectric layers have different effects on the current distribution and input impedance of the antenna. It is also found that the imaginary part of the input impedance as a function of antenna length has two zero points, where the first and second zero points correspond to a half-wavelength antenna (series resonance) and a full-wavelength antenna (parallel resonance), respectively. It is indicated that when the thickness of the dielectric layers or the antenna height changes, variations on the resonance length of the antenna are observed by examining the imaginary part of the input impedance.

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.

With the rapid development of the economy, the scale of transmission networks has been expanding, bring higher demands and challenges on transmission line operation and maintenance. In this paper, the multi-rotor unmanned aerial vehicles (UAVs) safety inspection rules and automatic detailed inspection methods for transmission towers are studied. The theoretical model of multi-rotor UAVs of transmission lines inspection is established. The imaging calculation range of multi-rotor UAV-equipped cameras is determined. According to the inspection theory model, the flight safety judgment standard is designed, and the key parts of the transmission lines that need to be inspected are determined according to the accurate model of the transmission tower. Then the inspection waypoints are manually operated, and the photographing position and angle of each waypoint from the flight control are recorded through the waypoint planning function. Finally, the waypoints are connected in order, and the inspection route is automatically generated to achieve automatic detailed inspection. The inspection efficiency, error analysis and position accuracy comparing the proposed method with some state-of-the-art methods have been evaluated. The results show that the position error of UAVs automatic detailed inspection is less than 10 cm. The error of height is between 1.26 and 1.76 meter. Compared with the traditional manual inspection, the efficiency of multi-rotor UAVs automatic detailed inspection can be increased by 57.98%~62.88% and can be applied to large-scale inspection of transmission lines.