Vortex beam heating is a research hotspot in ionospheric heating experimental technique.The existing research work focuses on the analysis and interpretation of experimental phenomena

while there are few discussions about the array feeding design method.Based on the Fresnel diffraction theory

the analytical expression of propagation characteristics of vortex beam in free space is deduced

as the inspection basis for the array feeding design method in the vortex heating mode.According to the Helmholtz equation of magnetic vector potential

the calculation formula of array feeding distribution for arbitrary order Laguerre-Gaussian vortex beam is derived.Then the formula is verified by the results of the existing literature.This provides the theoretical guidance for the array feeding design.By introducing the concept of sparse array

a design method of array feeding is presented

which is simple

convenient

practical and can be applied to any planar array.Simulation results demonstrate the effectiveness of the method.