Initial Results from The Plasma Antenna Test Setup

This paper presents initial results from the operation of a laboratory prototype plasma antenna. The device consists of a plasma column with cold electrons (T_e <= 4 eV) and density in the range 10⁹-10¹¹ cm^-3. A coupling loop connects a low power (< 5 W) RF signal to the column. This signal is received by a dipole receiver in the near field of the antenna. A second coupling loop can be moved along the plasma column to measure the phase of surface waves excited along the length of the plasma. We measured the dispersion of the plasma surface waves and the near field azimuthal antenna pattern over a range of input ionization power and a frequency range from 5- 400 MHz covering the VHF and lower UHF. It was found that the plasma antenna operated similar to a thin wire metal antenna with respect to frequency resonances corresponding to the length of the plasma column, but had a somewhat altered spatial directionality which changed to some extent with changing plasma density. These initial measurements demonstrate 1) that the plasma column operates as an antenna and the operation overlaps with a conventional metal antenna, and 2) changing the characteristics of the plasma column changes that operation.