Effect of subreflector displacement induced aberrations for dual-reflector antenna

The main purpose of this study is to investigate the effect of subreflector displacement for dual-reflector antenna. In this paper, the effect of misalignment of subreflector on path length difference is analyzed. By geometrical optics, the descriptions of path length difference due to the three kinds of subreflector displacements for dual-reflector antenna are re-expressed approximately as the Seidel aberration form. From the expressions it is seen that the path length difference due to axial translation of subreflector has the aberration features of spherical, focus and piston, and the path length difference due to lateral translation of subreflector has the aberration features of tilt and coma, and the path length difference due to rotation of subreflector also has the aberration features of tilt and coma. The effects of aberrations and displacement of subreflector on gain and pointing of a 26 m reflector antenna are analyzed. The results indicate that the effects on electromagnetic performance caused by the subreflector displacements are similar as that caused by the corresponding aberrations.