Reduction of the radar cross section of a moderate cylindrical structure using central impedance loading

A theoretical study on the minimization of the radar cross section (RCS) of a cylindrical structure of moderate radius centrally loaded by a lumped impedance that is illuminated by a plane electromagnetic wave at normal broadside incidence is presented. Expressions for the induced current on the surface of the cylinder and for the RCS are obtained, and an equation for the optimum loading impedance that minimizes the RCS for moderate cylinders is also derived. The reduction of the RCS is achieved because the impedance that centrally loads the cylinder reduces the superficial current and consequently the RCS. The current and impedance equations are derived using the Hallen´ method for calculating the current distribution in antennas. Computed curves of the induced current distribution in the cylinder and of the RCS are presented and experimental results for moderate impedance loading of dipoles not much longer than λ/2 are compared with the theoretical computations. For such dipoles, the broadside RCS can be reduced by 30 to 40 dB with appropriate passive center loading.