| Summary: | A novel 2×2-element corporate-feed horn sub-array antenna for the 77-GHz band is proposed in this paper. The stair-stepping horn is employed instead of a traditional pyramid horn to reduce the profile of the array. A set of composite structure composed of waveguide divider and cavity is designed and fabricated integrally with a computer numerical control milling technique to simplify the feed-network. Most of all, a metallic cross bar with the wall is innovatively loaded to reduce the mutual coupling and suppress the side lobe level of the sub-array. Measured results show that the proposed antenna achieves a -10 dB |S<sub>11</sub>| with a bandwidth of 72-85 GHz which is corresponding to 16.6%. Moreover, the average gain of the antenna is about 19 dB, and the side lobe level of the antenna is less than -9.3 dB within the working band.
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