An expression is derived for the driving point admittance of an infinite, perfectly conducting cylindrical antenna excited by a finite uniform gap and immersed in a lossy, compressible, isotropic plasma. This expression is based on the twin assumptions that the gap width is much smaller than the wavelength of the plasma (electroacoustic) wave and that the radius of the antenna is much smaller than the wavelength of the electromagnetic wave; it is similar in form to the corresponding expression for an infinite antenna in free space, and it is obtained in much the same manner. Conductance and susceptance curves computed from the admittance function are in good agreement with those obtained numerically by other authors for f ≥ 0.7 fP. The behavior of the admittance function at frequencies in the neighborhood of the plasma frequency depends mainly on the electron – neutral particle collision frequency, not the plasma temperature. In general, the effect of the temperature is quite small, although a temperature-related effect can produce large admittance values in very low-loss plasmas at frequencies well below the plasma frequency (f ~ 0.03 fP for T = 1500 °K). This investigation supports the view that the propagation constant of the current along a cylindrical antenna in a compressible plasma is nearly equal to the plane-wave propagation constant in an incompressible plasma.
