BG0AUB Hello Zhaofeng, the use of a conductive support, diameter < 0.1 wavelenght, INSIDE a helix is perfectly OK!. SWR may change a little bit, but will be good. The helix construction shown by G4SDG on the 1st picture in the other thread "DIY Helix for 2.4 GHz uplink . Can I use 5mm copper tubing?" is a very good example how to do it, in my opinion. See also the examples and explanation from G8AWB in the same thread.
You can use 10mm x 10mm square aluminum support tube which is light and strong.
Use only a few (nylon/teflon) vertical supports, exactly as seen in that picture and do not use any other support fixing the helix wires. This is to avoid degradation of the beam pattern.
I have written a "How-To-Construct a helix" document with a lot of practical information, that I can provide to you (and any other interested)!.
You probably know that this type of helix has less gain than a small offset dish with a small helix- or patch feed. My 1.0m wide offset dish with dualband helix/LNB-feed is putting out a very nice signal to QO-100 , but smaller dishes working equally good.
73 s Ed PA1EW