During its design phase, the JET ITER-Like ICRF antenna array has been modeled in great detail with the 3D electromagnetic software CST MICROWAVE STUDIO®. The resulting rf field and current density patterns have guided the optimization of the antenna feeder shapes, leading overall to a strong reduction (~25%) of the maximum electric field, and to a factor-of-three reduction of the inhomogeneity of rf current at the matching capacitors. The computed frequency response of the array is now used in matching studies and development of a control algorithm. Comparison with the experimental frequency response of the High Power antenna Prototype developed by ORNL and PPPL shows fair agreement.