Focal region characteristics of focused array antennas

The effects of focused aperture amplitude tapering, both direct and inverse, on axial forelobes and aftlobes are investigated. Taylor tapers give low sidelobes but high forelobes and aftlobes, plus a modest gain degradation. Inverse tapers give low forelobes and aftlobes but high sidelobes and large gain degradation. Uniform excitation gives comparable axial and transverse subsidiary lobes, and is probably the best choice. Focal shift, where the peak axial power density occurs between the aperture and the phase (geometric) focus, due to the
1/R^{2}
factor, is accurately calculated for a uniform square aperture. Since peak axial power density available from a focused aperture depends only on aperture size in wavelengths and on distance, these focal shift results allow system trade-offs to be made.