Discussion about the effect of the OAM topological charge on a microwave link budget

In order to clearly analyze the fundamental changes when dealing with OAM waves, we try to simplify a conventional point to point microwave link. The geometrical configuration is then reduced to face to face, co-axial, annular antenna arrays. Under assumptions of uncoupled elementary sources and ideal Beam Forming Network, the global link budget is derived from an original asymptotic development and analytically exhibits the topological charge effect. A new expression for antenna´s Gain is then obtained, surprisingly increasing with the topological charge l. The specific decrease previously discussed by Tamagnone with respect to the distance is found again.