Design of Alvarez Beam Scanning Reflectarray With Inversely Proportional Focal Length
Mustafa K. Taher Al‐Nuaimi, Shi-Long Zhu, William G. Whittow, Rui‐Sen Chen, Guan‐Long Huang, Abdelhady Mahmoud
Abstract
In this letter, a beam scanning Alvarez reflectarray (RA) metasurface with its focal length ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> ) inversely proportional to the phase distribution on the Alvarez RA aperture is presented for ±45° beam scanning coverage and less than 3 dB gain loss. The beam scanning mechanism is based on mechanically tilting the Alvarez RA panel to the desired direction to steer the beam. Compared to a conventional RA where <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> is directly proportional to the parabolic phase distribution, the proposed Alvarez RA shows a wider 1 and 3 dB gain bandwidth, higher aperture efficiency (AE <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">)</i> , and wider scanning range with less than 3 dB gain loss. The proposed RA has adopted an Alvarez phase distribution, which is a summation of two shifted cubic phase profiles. Pancharatnam– Berry (PB) meta-atoms of subwavelength periodicity were utilized to provide the 360° phase range and to enhance the bandwidth of the RA. An Alvarez RA consisting of 38 × 38 PB meta-atoms has been designed, fabricated, and tested for ±45° beam scan coverage with less than 3 dB gain loss. The simulated and measured results show that the gain of the proposed Alvarez RA metasurface is 29.1 dBi at 19.5 GHz, which corresponds to an AE of 44.2%. The 3 dB gain variation of the Alvarez RA is from 15 to 23.4 GHz, which corresponds to a 3 dB gain bandwidth of 43.7%. The 1 dB gain bandwidth was 27.8% from 17.3 to 22.9 GHz.