US Patent 6902149 Vulnerable target protection system

A defense barrier for protecting a target from critical damage from the impact of a predetermined group of aircraft comprises: a plurality of towers spaced from the target, each tower being spaced from a neighboring tower by a distance less than the wingspan of an aircraft in the predetermined group of aircraft having the smallest wingspan in the group; each tower being spaced from the target at least a distance d given by the formula: d=h/tan(theta) where h is the height of the tower and theta is the smallest vertical approach angle of any aircraft from the predetermined group of aircraft sufficient to inflict critical damage to the target.