Theory of a Square Loop Antenna in an Anisotropic Magnetized Plasma

As a typical configuration of antennas, square loop antenna will have applications in future very low frequency (VLF: 3–30 kHz) space-borne transmitting system. In this article, a VLF square loop antenna placed in an anisotropic magnetized plasma is studied by the combination of numerical and analytical methods. Kernel function for a square loop antenna with arbitrary orientation is derived by using relative coordinates. With the help of a phase-sequence expansion, the coupled integral equations are decomposed into several independent phase sequences so that they can be solved individually with the method of moments (MoM). Computational results show that the mutually perpendicular arms of the loop have different current distributions due to their distinct wavenumbers. Also, current moments on the arms decay with the geomagnetic dip angle while the input impedance increases as the dip angle, operating frequency, or the half-length rises. By using commercial software CST Studio Suite, a comparison is made between the simulated results and the computed results to show the correctness of the proposed method. This work may provide theoretical instruction to design and application of a practical VLF space-borne transmitting system in near future.