waveguide components

I want to construct a curved line with a WR90 waveguide (L=1m)
what is best and accurate procesure of Manufactureing it?
can ant one help with a refrence

Find a book by MOreno: MIcrowave component design,or Harvey: MIcrowave Engineering.

Use the largest curvature radius, or be ready to include correction stub or iris to compensate.

You can fill it full of sand, ice, or other incompressible material and bend it on a mandrel. Then you pour out the material and the cross-section has not collapsed on you.