Theory of Arbitrarily Oriented VLF Linear Antennas With Lumped Loadings in Ionospheric Plasma

For very low frequency (VLF: 3–30 kHz) space-borne transmitting systems, the antenna loading technology provides a new technical scheme in boosting the antenna efficiency by optimizing its current distribution and input impedance. This communication studies the theory of VLF linear antennas applied with the lumped loadings in the ionospheric plasma. By considering the influences of ordinary and extraordinary waves and using Kirchhoff’s laws, the integral equation of the antenna under the effect of lumped loadings in an ionospheric plasma is derived and calculated by the method of moments (MoM). Calculations indicate that after loading capacitance, the overall current of the antenna increases while the input impedance decreases. It is also found that loading resistance and inductance will make the antenna current smaller. Theoretical results are compared with those simulated by commercial software, and the agreement demonstrates the validity of the approach. By comparing the input impedances of loaded and unloaded antennas, we observed that loaded antennas are more efficient than unloaded ones when the capacitance is appropriately deployed.