Cavity-backed apertures (CBA) are encountered as parts of any airborne or spaceborne radar targets. Most familiar of them are, probably, air inlets and engine tubes, known to contribute a great deal to radar cross section (RCS) of jet aircraft. In the present study, the dual-series-based solution is obtained for the scattering of an E-polarized plane wave from the cavity-backed aperture which is formed by a slitted infinite circular cylinder coated with absorptive material. The material coating can be done on the inner or outer surface of the cylinder. For both cases, numerical results are presented for the RCS and comparisons of the suppression of RCS are given for two different realistic absorptive materials.