A Double-Layer Metal-Only Transmitarray for Beam Scanning

A novel metal-only transmitarray (TA) operating in linear polarization in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$X$</tex-math></inline-formula> band for beam scanning is proposed in this article. It is composed of metal-only unit cells with a double-layer structure, which obtains a complete 360<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> phase shift range with low loss by adjusting the length of interleaved slots etched on the thin metal sheets. The feed displacement technique is used as a feasible mechanical control approach for beam scanning, and bifocal phase distribution is designed for the TA to improve the gain roll-off and the scanning coverage. In order to demonstrate the design scheme, a TA prototype consisting of 24 × 24 unit cells has been fabricated and measured. The measured results show that the proposed TA can achieve a maximum gain of 27.8 dBi at 10 GHz, and a scanning coverage from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-25^{\circ }$</tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$+25^{\circ }$</tex-math></inline-formula> with sidelobe level lower than 10 dB.