Radius of the rim of a paraboloidal dish

Description

The elliptic paraboloid is shaped like an oval cup and can have a maximum or minimum point. In a suitable coordinate system with three axes x, y, and z, it can be represented by an equation witch constants dictate the level of curvature and the way that the paraboloid opens upward or downward.
Revolving a parabola around its axis the obtained surface is a paraboloid of revolution (a=b). It is the shape of the parabolic reflectors used in mirrors, antenna dishes.

Related formulas

Variables

RRadius of the rim (m)
FFocal length (m)
DDepth of the dish (measured along the axis of symmetry from the vertex to the plane of the rim) (m)