| CPC E21B 7/15 (2013.01) [H01P 3/123 (2013.01)] | 30 Claims |

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1. An apparatus comprising:
an outer tube having an inner surface, an inner diameter, and a length; and
at least one inner tube having an inner surface, an outer surface, an outer diameter, and at least one corrugation feature configured to propagate a millimeter electromagnetic wave and formed on the inner surface and extending along a length of the at least one inner tube, and the at least one inner tube is positioned within the outer tube and the outer diameter of the at least one inner tube is less than the inner diameter of the outer tube, wherein the at least one corrugation feature includes at least one groove adjacent to at least one ridge and a width of the at least one corrugation feature is less than a sixth of a wavelength of the millimeter electromagnetic wave.
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