Reflectarray antenna

Lore & Background

The reflectarray combines features of a parabolic reflector and a phased array. Its unit cells are typically backed by a ground plane, and each cell introduces a phase delay to the reflected signal. The phase distribution on the surface is calculated to produce a constant phase in a plane normal to the desired beam direction. For a feed horn at (0,0,F), the optimal phase shift for a boresight beam is given by Δϕ(xₘ,yₘ) = (2π/λ₀)√(x²+y²+F²). The feeding antenna is often offset to prevent blockage of the beam, which requires altering the phase distribution. A fixed reflectarray has a single beam direction per feed and cannot be reconfigured, making it suitable for point-to-point communications or satellite coverage of a specific geographic region. A reconfigurable reflectarray uses electronically controlled unit cells, implemented with PIN diodes, liquid crystal, or novel materials, though each method introduces loss and linearity concerns.

Reader's Guide

The reflectarray is notable for achieving beam focusing and steering with a planar, low-profile structure, offering an alternative to bulky parabolic dishes. Its aperture efficiency and gain depend on factors such as the angle of incidence on unit cells, spillover, illumination uniformity, and phase quantization errors. In satellite communications, multiple beams per feed are possible, sometimes using different frequencies and polarizations, such as in four-color frequency reuse schemes. Circular polarization is commonly used to mitigate atmospheric depolarization. Dual-band reflectarrays handle separate uplink and downlink frequencies. A bifocal reflectarray has two principal foci for simultaneous operation with two feeds. A dual reflectarray uses two stages of reflection to achieve quasi-optical magnification, narrowing the beam. The design of phase distributions must account for phase derivatives consistent with ray incidence angles. The reflectarray's ability to produce fixed or reconfigurable beams makes it relevant for point-to-point links and satellite coverage, while its thin form factor supports integration into space-constrained platforms.

Did You Know?

• The phase distribution on a reflectarray can be altered to steer the beam direction by applying a progressive phase shift.
• Reconfigurable reflectarrays use PIN diodes, liquid crystal, or novel materials for electronic beam control.