OT: High Frequency coax?? Copper tubing??


This question is related to my Rohde and Schwarz SMS Signal Generator (rescued from a Rubbish Dump). There is some type of coax or copper tubing in this Signal Generator which I am unsure about. There are several photos in the following Album ... https://groups.io/g/TekScopes/album?id=130642 .... specifically photo "Rohde and Schwarz.... 1007" Although this is not related to my current problem with its PSU, I would like to understand what this tubing is.
My Google searching has led to discussions about limitations of coax and BNC's, and waveguides at GHz frequencies etc, but I do not understand this in the context of a 520MHz Signal Gen and that the the lower tubing in photo "1009" terminates on the rear panel at a BNC.
Any explanations or 'pointing me in the right direction' would be appreciated.
My apologies if this is too far off-topic, but this is one Forum I trust where the appropriate expertise resides..
Melbourne, Australia

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