Characterization of carbon-attenuator coatings for helical traveling wave tube applications

Attenuator coatings of carbon were deposited on alumina support rods by pyrolytic deposition, aquadag coating and arc discharge to absorb the reflections and to improve the stability of a helical traveling wave tube. An experimental set up involving a narrow-height wave-guide with a hole was used to measure the attenuation of the coated rods at 6.0 GHz frequency by carrying out reflection and transmission measurements using a scalar network analyzer. The same structure was also simulated by using a high frequency structure simulator (HFSS). Results indicate that the aquadag-coated films provide a maximum loss or absorbance and are suitable as the attenuator coating. The simulated results by HFSS agree well with the experimental observations.