| 摘要 |
A rotational antenna has a circular portion having a disc-like shape and a cylindrical portion connected to the central portion of the circular portion, and rotates in a direction perpendicular to the sheet with the cylindrical portion serving as an axis. By driving a motor, the motive power is transmitted via a motor shaft and the cylindrical portion to the rotational antenna, thereby rotating the rotational antenna. A bearing serves the function of a spacer between the cylindrical portion and a waveguide. A spacer is attached on an upper surface of the circular portion. The dimension in the direction of height of a spacer is greater than the distance in the direction of height between a bottom plate and a portion in the vicinity of the central portion of the rotational antenna. Thus, the rotational antenna deflects from its central portion toward its outer edge portion, and is fixed with respect to the up-down direction by spacers and the bearing.
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