Norio Miyahara

Deployable antenna with 10-m maximum diameter for space use

This paper describes a large deployable antenna which is used at L-, C-, and Ka-bands on an artificial satellite in space. The main reflector with 10-m maximum diameter is formed using the tensioned truss concept which was proposed by one of the authors. The mechanical structure of the antenna is briefly explained and a more detailed description given of the electrical design of the antenna and the verification method of electrical characteristics. This antenna was successfully launched and deployed in space in 1997 and is used for a Space VLBI mission.

A millimeter-wave cassegrain antenna using shaped beam waveguide feed

As a way to increase the efficiency of the focused beam-fed Cassegrain antenna with a large aperture for use at millimeter-wave frequencies, a method is proposed for shaping the surface of two focusing reflectors in the focused 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 deformation of the reflector surface on the radiation characteristics. Both the sub- and main reflectors have quadratic surfaces. The aberration in the main reflector due to self weight deformation can be corrected with the deformation of the subreflector in the homologic design. Hence, in order to validate the 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 focusing reflectors is applied to the new 10-m antennas for the millimeter-wave interferometer of Nobeyama National Observatory (model No. 6). The alignment errors in the parallel shift in three axis directions and the rotating motion about the axes are assumed, and the aberration and the gain degradation are quantitatively investigated when each focusing reflector is deformed. It is shown that the grain degradation is small in the range of realizable alignment errors and that the method of shaping the surfaces of two focusing reflectors is effective as a reflector shaping method for a millimeter-wave large-aperture antenna.

An analysis of multimode conical horn antennas with flare-angle changes by using generalized telegraphist's equation

A multimode conical horn antenna can realize a rotationally symmetric radiation pattern with a low cross polarization level by exciting a dominant mode and higher-order modes with appropriate composition ratios. One of the mechanisms to generate the higher-order modes is a flare type in which the flare angle of the horn is varied. This structure is simple and can be made only with a conductor. In this paper, an analysis of a flared multimode conical horn antenna using a generalized telegraphists equation is described. In the present method, many higher-order modes are considered in the telegraphists equation; the results are confirmed to agree well with the measured results and thus the validity of the method is proven. A design method based on the presented analysis procedure is also described. It is confirmed that sufficient accuracy can be obtained in this design.

A patterning method of polarization grids on a reflector using reflector surface developing technique

This article proposes a patterning method of polarization grids on a reflector using reflector surface developing technique for gridded reflector antennas. Gridded reflector antennas have excellent cross-polarization suppression characteristics caused by their polarization grids on a reflector. The proposed grid patterning method is simple to transcribe a plane grid pattern onto a curved reflector surface, being different from conventional complicated methods such as a direct photoetching method by N/C-driven laser system. A key technology for plane pattern design to obtain a desired pattern on a curved reflector surface is described. The method is evaluated through appropriate models and is verified by a measured radiation pattern.