| 摘要 |
The invention provides an inner-feed-type planar antenna of single-layered structure excited by an axially symmetric mode for propagating radio waves from the center toward the outer periphery within a propagation layer having an antenna surface. If the planar antenna is used for transmission, the antenna is provided with a plurality of coupling slots formed and arrayed in one surface of an axially symmetric mode waveguide member in such a manner that the coupling factor of the external radiation is high at the outer periphery and becomes successively lower as the center is approached. A spiral- or ring-shaped terminating slot is provided in the antenna surface at the outer portion of the axially symmetric mode waveguide member. A region not coupled with the outer portion is provided at the center of the antenna surface. Furthermore, the planar antenna is provided with a reflector member arranged along the terminating slot for reflecting a propagating radio wave between the inner and outer portions of the axially symmetric mode waveguide member. Accordingly, a comparatively flat aperture distribution in which the electromagnetic field is uniform can be obtained. In addition, by providing the central portion with a non-radiating region, long-line effect is suppressed and bandwidth enlarged.
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