Reflectarray antenna

. Structure showing unit cells. This antenna has fixed cell delays, configured by different cutout sizes in each cell, as can be seen in the top-right inset. Larger cutouts produce the dark rings visible in the overview. A reflectarray antenna (or just reflectarray) consists of an array of unit cells, illuminated by a feeding antenna (source of electromagnetic waves). The feeding antenna is usually a horn. The unit cells are usually backed by a ground plane, and the incident wave reflects off them towards the direction of the beam, but each cell adds a different phase delay to the reflected signal. A phase distribution of concentric rings is applied to focus the wavefronts from the feeding antenna into a plane wave (to account for the varying path lengths from the feeding antenna to each unit cell). A progressive phase shift can be applied to the unit cells to steer the beam direction. It is common to offset the feeding antenna to prevent blockage of the beam. In this case, the phase distribution on the reflectarray surface needs to be altered. A reflectarray focuses a beam in a similar way to a parabolic reflector (dish), but with a much thinner form factor.

. Structure showing unit cells. This antenna has fixed cell delays, configured by different cutout sizes in each cell, as can be seen in the top-right inset. Larger cutouts produce the dark rings visible in the overview. A reflectarray antenna (or just reflectarray) consists of an array of unit cells, illuminated by a feeding antenna (source of electromagnetic waves). The feeding antenna is usually a horn. The unit cells are usually backed by a ground plane, and the incident wave reflects off them towards the direction of the beam, but each cell adds a different phase delay to the reflected signal. A phase distribution of concentric rings is applied to focus the wavefronts from the feeding antenna into a plane wave (to account for the varying path lengths from the feeding antenna to each unit cell). A progressive phase shift can be applied to the unit cells to steer the beam direction. It is common to offset the feeding antenna to prevent blockage of the beam. In this case, the phase distribution on the reflectarray surface needs to be altered. A reflectarray focuses a beam in a similar way to a parabolic reflector (dish), but with a much thinner form factor. \frac{2\pi}{\lambda_0} \left(r_{mn} - R_{mn}.r\right) - \Delta \phi_{mn} = 2 \pi N where \lambda_0 is free space wavelength, r_{mn} is the position vector of the {mn} th element/unit cell relative to (0,0,F) , F is the focal length, R_{mn} is the position vector of {mn} th element relative to the origin (0,0,0) i.e. centre of the reflectarray, r is the direction vector of the desired pencil beam, N = 1,2,3,... , and \Delta \phi_{mn} is the phase shift introduced by {mn} th unit cell of reflect array to its reflected field relative to the incident field. For a feed horn located at (0,0,F) , the formula for the optimal phase distribution on a conventional reflectarray for a beam in the boresight direction is given by: \Delta \phi(x_m, y_m) = \frac{2\pi}{\lambda_0}\sqrt{x^2 + y^2 + F^2} where \Delta \phi(x_m, y_m) is the phase shift for a unit cell located at coordinates (x_m, y_m) . s of a reflectarray antenna operating at 12.5 GHz.

Text derived from https://en.wikipedia.org/w/index.php?oldid=1209417156 under CC BY-SA 4.0; modifications have been made.