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 ^o 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-dB 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 sub-wavelength periodicity were utilized to provide the 360 ^o 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 ^o 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 GHz 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 GHz to 22.9 GHz.