Design of Alvarez Beam Scanning Reflectarray With Inversely Proportional Focal Length

In this letter, a beam scanning Alvarez reflectarray (RA) metasurface with its focal length (F) inversely proportional to the phase distribution on the Alvarez RA aperture is presented for +/- 45 degrees 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 F 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), 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 degrees phase range and to enhance the bandwidth of the RA. An Alvarez RA consisting of 38 x 38 PB meta-atoms has been designed, fabricated, and tested for +/- 45 degrees 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.