A millimeter-wave cassegrain antenna using shaped beam waveguide feed

As a way to increase the efficiency of the focused beam-fed Cassegrain ante nna with a large aperture for use at millimeter-wave frequencies, a method is proposed for shaping the surface of two focusing reflectors in the focus ed beam waveguide feed. The reflector surface shaping method is presented. Since the reflector is used at millimeter-wave frequencies, it is necessary to take into account the effect of the aberration caused by the deformatio n of the reflector surface on the radiation characteristics. Both the sub- and main reflectors have quadratic surfaces. The aberration in the main ref lector due to self weight deformation can be corrected with the deformation of the subreflector in the homologic design. Hence, in order to validate t he present beam shaping method, it is necessary to evaluate the effects of the aberration caused by the alignment error of each focusing reflector on the radiation characteristics. In this paper, a method of shaping the two f ocusing reflectors is applied to the new IO-m antennas for the millimeter-w ave interferometer of Nobeyama National Observatory (model No. 6). The alig nment errors in the parallel shift in three axis directions and the rotatin g motion about the axes are assumed, and the aberration and the gain degrad ation are quantitatively investigated when each focusing reflector is defor med. It is shown that the grain degradation is small in the range of realiz able alignment errors and that the method of shaping the surfaces of two fo cusing reflectors is effective as a reflector shaping method for a millimet er-wave large-aperture antenna. (C) 2000 Scripta Technica.