Thermal properties and power capability of helix structures for millimeter waves

The thermal properties of materials, that can be used for high power helix structures, were evaluated experimentally with equipment that incorporated an infrared microscope for temperature measurements. The interface heat transfer properties between such materials were measured as a function of contact pressure and for different surface finishes. In addition the thermal conductivity of suitable ceramic materials, such as anisotropic Boron Nitride, Beryllia and Diamond was measured as a function of temperature. Millimeter wave helix structures for 40 GHz to 50 GHz were constructed for thermal evaluation with these materials. The Diamond supported helix structure demonstrated a power handling capability of 165 Watts/in with an average helix temperature of 380°C, indicating that helix traveling wave tubes can be designed for power levels of 100 Watt to 200 Watt CW in the 40 GHz to 50 GHz range using such a structure.