Low Frequency Radio Transmission Through a Collisional Plasma via Antenna Impedance Matching

Radio communication through a layer of plasma is a common requirement in several applications, particularly for high-speed vehicles traveling in the Earth’s atmosphere. Plasma sheaths generally act as a shield that blocks radio frequencies below the plasma frequency. We show that a finite collision rate in the plasma results in a higher degree of transmission for low frequency signals that would have otherwise been shielded. Furthermore, it is demonstrated that reflections at the air-plasma interface can be minimized by utilizing the near-field impedance properties of an antenna. The transmission coefficient through a homogenous plasma slab is evaluated analytically for an incident plane wave and for a small loop antenna that is placed close to the plasma. It is shown that at frequencies considerably below the plasma frequency, the fields from a loop antenna can transmit through the plasma several orders of magnitude more efficiently than a plane wave. The results suggest that an antenna’s near-field impedance properties can thus be exploited to enhance low frequency radio communications through collisional plasma sheaths.