[en] In the Doublet IIA high power rf heating experiments, a slow wave is launched by an electrostatic antenna above the lower hybrid frequency. Such an antenna has been proposed previously for generating a well-defined large parallel wavenumber spectrum. In the present experiments, a total of six structures with n/sub parallel/ from 11 to 16 at 800 and 915 MHz at power up to 100 kW/structure are being used. The coupling and radiated spectrum are analyzed using the theory developed for these antennas. They are found to be insensitive to changes in plasma parameters