A theory of the attenuator-coated helical slow-wave structure of a traveling-wave tube

A theory of the attenuator-coated helical slow-wave structure of a traveling-wave tube has been developed by considering the helix turns to be effectively shorted by a resistive coating. Power propagating down the structure is interpreted for the interaction impedance in the presence of the attenuator-coating losses. The dependence of the attenuation and phase propagation constants as well as the interaction impedance on the surface resistivity of the coating, the operating frequency, the thickness/proximity of the envelope, the permittivity of the dielectric, and the pitch of the helix have been studied for two situations in which the attenuator coating is applied: (1) inside a dielectric tube that the helix fits into, the whole enclosed in a metal envelope: and (2) over a dielectric tube enclosure for the helix.<
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