Theory of a VLF Circular-Loop Antenna in an Anisotropic Magnetoplasma

The circular-loop antenna is one of the most basic antenna forms for very low frequency (VLF: 3–30 kHz) space-borne transmitting systems. However, the theoretical progress of the loop antenna in an anisotropic plasma is slower than that of the linear antenna due to its complexity. This article studies the theory of a VLF circular-loop antenna located in an anisotropic magnetoplasma. The current integral equation of the current is formulated by deriving the exact kernel function and boundary condition. By taking both the effects of O-wave and E-wave into consideration, the current distribution and input impedance of a circular-loop antenna are solved via the method of moments along with the numerical techniques. The results show that the current amplitude decreases with the loop radius. As the size of the loop increases, the current distribution resembles a cosine function with its phases jumping at several positions. Moreover, the input impedance of the antenna increases as the radius and operating frequency increase. The proposed approach is validated by comparing the computed impedance with that simulated by the commercial software FEKO. The preliminary study of VLF loop antenna theory can offer theoretical guidance in antenna design and efficiency improvement for actual VLF space-borne transmitting systems.