| 摘要 |
<p>A multiple-frequency feed assembly for an antenna system having two coaxial cavities, with a smaller, high-frequency cavity mounted coaxially within a larger, low-frequency cavity. A separate rotatable probe is mounted within each cavity. The smaller cavity is mounted within the larger cavity by any of several structures, such as a ring-shaped spider, a ring-shaped spacer in the form of a planar washer, or a harp extending rearwardly in the larger cavity. In all of the embodiments, a continuous, uninterrupted signal path is provided within the low-frequency cavity, around the high-frequency cavity, for conveying incident electromagnetic signals to the low-frequency probe mounted at the rear of the low-frequency cavity. In other embodiments, the feed assembly is adapted to detect incident electromagnetic signals in a third band of frequencies, lower than the low-frequency band, using a third probe located within the low-frequency cavity, immediately adjacent to the high-frequency cavity. This third probe preferably is aligned circumferentially with a conductor for conducting the detected high-frequency signal from the high-frequency probe to the exterior of the feed assembly. In an independent feature of the invention, a dielectric cover for the low-frequency cavity incorporates one or more integral dielectric blocks that function as quarter-wave plates for transforming incident circularly polarized electromagnetic signals in either or both of the low- and high-frequency bands into linearly polarized signals, for efficient detection by the corresponding probes.</p> |
