OH, I see!
I didn’t read that picture very well…
I’d take part of a Circle and Add a larger Plane (in Edit Mode) and Delete its Face and Subdivide it to match the Circle and then Bridge Edge Loops and extend outwards and inwards, something like this:

You can Add Edge Loops where needed and give it some thickness (it is sometimes easier to start 2 Dimensional and Extrude afterwards…)