Abstract: 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 6.0GHz 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.