Consider a lens of diameter d and a focal length f >> d. Let the cross-section area of the lens be S = N*λ^2. Let a plane wave be focused from S to an area S1=λ^2. Then, by the linear superposition principle the electric field intensity in the area S1 will be N times greater than it was in the original plane wave. This means EM wave intensity N^2 times greater in the area S1, which means N-fold increase of the power of the EM wave due to focusing. Is focusing a process that violates energy conservation?