Would you be able to achieve a strong enough structure if you instead of bracing it as shown go to a box section coming back from the original frame of sufficient thickness and cross section to eliminate the need for the additional bracing and gusset it as well as create a cross bracing in a geodesic design to make it rigid as well? Or, are you going to have to have a triangular brace tube as you are showing?
Just wondering if you could think further out of the box. Naturally, the end of the loop would probably need to be a tube or similar as bending into a curved hoop in box section isn't easy or practical. It can be done, just not ideal. You could even take the hoop and face it with a flat section if you wanted to match the profile of the hoop with a section of U channel with it cut and welded so the inside is a half round and outside face is a box section. That would further strengthen that part of the hoop, but merely for asthetics.
If you have access to fabricating equipment that can bend thick walled tubing, then go for it...
Just throwing out a different idea.
