An effective method is developed in order to reduce the part of the far sidelobes originating from the scattering of the struts in rotationally symmetric reflector antennas such as prime-focus or Cassegrain antennas. This method is based on completely eliminating the specular reflection from a strut and backscattering all incident power in the direction of incidence. A circulator in the feeding waveguide is employed to suppress the interference due to the wave scattered back into the feed horn. A theoretical approach is presented and applied to design struts of finite transverse size for reflector antennas with low far sidelobes. The measured pattern of a prime-focus paraboloidal antenna at 11.5 GHz is presented. It is found that with smooth struts the sidelobe level at 2-alpha (the flare angle of the radiation pattern due to the struts) is about -35 dB, whereas it is better than -48 dB with struts provided with a corrugation boundary. The sidelobe level caused by the struts in other planes of the radiation pattern is also significantly reduced.