The radiation pattern and induced current in a circular antenna with an annular slit

A finite plane antenna is considered which has holes on one side that act as sources of radiation and which is on the remaining parts of this side and on the whole other side perfectly conducting. The purpose of this paper is to develop an approximation method for the computation of the radiation pattern which works well if the finite plane and the distance of the holes from its boundary are large compared with the wave length. This is achieved by computing the radiation field of a corresponding infinite plane antenna and subtracting from it the field produced by the current induced in the infinite plane outside the finite plane antenna. Numerical results for the circular antenna with annular slit show that this approximation method is very satisfactory.