The admittance of an infinite cylindrical antenna in a lossy, compressible, anisotropic plasma

Abstract

An analysis of the current on an infinite cylindrical dipole antenna which is excited across a circumferential gap of nonzero thickness and immersed in a lossy, compressible magnetoplasma with its axis parallel to the static magnetic field is described. Some numerical results are presented for the antenna admittance for the sheathless case, where the uniform magnetoplasma is in contact with the antenna surface. The admittance values are obtained from a numerical integration of the Fourier integral for the antenna current, and are given for plasma parameter values typical of the E region of the ionosphere.The admittance values obtained exhibit a maximum slightly above the electron cyclotron frequency, and in this regard are similar to the admittance when the magnetoplasma is incompressible but separated from the antenna by a free-space layer (the vacuum sheath). In addition, the admittance is found to have a slight minimum at the plasma frequency and to have a more pronounced minimum at the upper hybrid frequency where also the susceptance changes sign, these minima not being significantly affected by the plasma compressibility or vacuum sheath. These features of the calculated admittances are found to have a qualitative resemblance to experimental results obtained from antenna measurements in the ionosphere.

Results from a swept-frequency ionospheric impedance probe

“…Miller used a concentric free-space layer or vacuum sheath to approximate the actual inhomogeneous sheath. In addition, it is interesting to note that, for the infinite antenna, the plasma compressibility causes an upward shift of the impedance minimum for the anisotropic plasma when there is no sheath (Miller, 1968) and may thus represent an equivalent capacitance.…”