The problem of electromagnetic waves diffraction on an perfectly conducting open-ended cylindrical surface is of great practical importance. The metal screens of a similar configuration are used as reflectors at the linear radiator, as screens for protection of instrumentation against external electromagnetic fields, as the device for decreasing mutual influence of low directional antennas and for other purposes. With the help of impedance loads it is possible to obtain the specific diagram of conductive objects scattering. In the impedance loads used nowadays (such as a ridge structure, the rectangular groove) there is a strongly marked dependence of an impedance size on an angle of incidence of electromagnetic waves. It is known [1], that in the semi-cylindrical concavity this dependence is not pronounced.

Note, that the essential change of a scattering field with the help of single impedance loads can be achieved only for objects with small electrical sizes. At sizes of object, considerably exceeding a wave-length, a great deal of impedance loads or allocated impedance must be applied, that is eventually one is forced to deal with arrays of impedance loads.