| Summary: | This article presents a double-layer four-corner-fed slotted waveguide sparse array antenna designed for the near-field-focused applications in the X-band. Generally, it is challenging to realize the ideal phase distribution of the near-field focused array antenna, especially for the near-field focusing array antenna with a focal distance less than 5λ. We propose a four-corner-feed structure associated with appropriate waveguide dimensions to realize approximately ideal phase distribution for a focus at 1.5λ. The sparse array based on the particle swarm optimization is adopted to suppress the sidelobes and the grating lobes on the focal plane caused by the residual phase errors. A test antenna is designed at the center frequency of 10 GHz, and is fabricated by Direct Metal Laser Sintering technique for demonstration. It is verified by the experiment that we achieve satisfying near-field focusing effects, especially in terms of the focal spot size and sidelobe levels on the focal plane 45 mm away from the antenna aperture.
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