Study of the Radiation Pattern of the Unipole Plasma Antenna

The dispersion of the axially symmetrical surface wave along the plasma column is studied. The wave number, deduced from the dispersion equation, is used to explain the fact that the plasma surface wave, with a frequency lower than the plasma frequency, propagates with a speed near that of the light along the plasma column, just as it travels along the metal- dielectric interface. That is to say, the plasma column can work as an antenna element. By using the methods of analyzing the antenna with an impedance distribution, the relationship between the parameters of the plasma and the radiation patterns of the unipole plasma antenna is revealed on the VHF band. The results indicate that, for a one-meter-long unipole plasma antenna, when n_e< 10¹⁸ m^-3 and 10⁶ Hz < v_m < 10⁹ Hz , its radiation pattern is similar to that of the metal antenna at the low side of the VHF waveband. When n_e > 2 times 10¹⁷ m^-3 and v_m < 10⁹ Hz, its radiation pattern is in conformity with that of the metal antenna at the high side of the VHF waveband.