The radiation pattern of a monopole antenna surrounded by commercial fluorescent tubes was measured in this article. Measurements were collected for two antenna frequencies and different discharge currents. The results showed that the antenna pattern depended on which plasma tube configuration was activated. Increasing and decreasing field-operating modes of the plasma antenna system were determined. These operating modes relied on the working frequency and the plasma tube configuration: if the distance between the tubes and the monopole antenna equaled a quarter of the wavelength, then the radiation field increased compared to a free monopole antenna; if this distance was shorter, then the radiation field declined rapidly.