Are you thinking of a tunnel covered with foliage...with gourds hanging down, flowers? I would call this a pergola. Build a wood structure with pressure treated 6X6 posts even 8X8 posts. Horizontals should be just as massive. 2X2's lap jointed together are gorgeous. These make a lattice work for the plants to climb. Stain the wood with a dove-gray transparent stain. Colors and paint are high maintenance. 4X4's are just too thin, for aesthetic reasons. What do you imagine? Fragrance, fruits, evergreen foliage? Your zone will dictate what you can grow and what you shouldn't grow.
To give you a couple of ideas, my favorite vine is Humulus lupulus 'Aureus'...Golden Hops Vine. Zone 6. This will die back in the winter making it easy to remove all the old vines and in the spring they come back with fresh vines and leaves. Trust me, this plant will cover the dimensions you are thinking about easily. Yes, if you've got females, they can be made into beer.
An evergreen flowering vine would be Akebia quinata. Very hardy for zone 5. Very little pruning after flowering would be necessary. The flowers are beautiful observed from below in a pergola.
A plant at every other post would be enough. A good design of your structure should support snow and an evergreen plant. Otherwise, most vines will die back during the winter and snow will not be a problem.
Kiwi is an excellent idea.
Send a picture of a structure you like and I can help make suggestions. Also where you plan to build this, wind and sun orientation, path material...your zone.
UPDATE: This is going to be a major structure in your landscape. If you want kiwi and grapes, it should be quite substantial to support the weight all year. Posts, 6-8' span. I wouldn't use the field wire unless you have the dimensional lumber as the basic structure.
Do make drawings to scale for this, otherwise it will look unprofessional? I wouldn't think of building something like this without using graph paper, considering the entire backyard and done to scale. Kiwi and grapes would be all I would plant. Actually, I'd do one or the other. Pruning will be a big deal for both these plants and they are a bit different from each other. Planting one species including males and females of the species for the kiwi will look spectacular. Too many different kinds of vines will look chaotic and the maintenance will become a nightmare.
Keep the structure uniform around the arc of the semi-circle. Allow a gap at the top of the semi-circle to open out onto a gravel patio, here you can build separately, an overhead structure with its own dimensions. Curves, circles are fine but limit the curve to the path and try to make at least your wider, patio area to have 90 degree angles.
Are you good with carpentry? If not, I would highly recommend getting bids from professionals on this project. Done right, you will increase the value of your home and actually make money when you sell your home. If you've got your ideas in your head, put it on paper, take a picture and send it to me. Make it to scale. Include your home, property lines, a few elevations to show high and low points, utilities, plant beds, lawn areas, North/South, scale, wind direction, fences outbuildings, views you like, views you don't, areas where you would like more privacy...it doesn't have to cost an arm or leg. You just want whatever you spend to work for you. Go on the internet and get ideas. Send those as well.
Think about what you'd like if money were no object. Adjusting to fit your budget later one usually gets far more and a better product. You are going to have to do some homework here. I can help you make good decisions. This process is very enjoyable and will cost you less in the long run.
