Reflectarray Antennas

5Bandwidth of Reflectarray Antennas

As discussed in the earlier chapters, the reflectarray combines the numerous advantages of both antenna arrays and reflectors and creates a low‐profile, low‐mass, and low‐cost antenna with a high gain. Despite the numerous advantages this hybrid configuration can offer, the reflectarray antenna suffers from a major limitation: an inherently narrow bandwidth. The bandwidth of reflectarray antennas depends on its element, aperture size, focal length, and so on, and typically does not exceed beyond 10%. In this chapter, we will study the fundamental physics that determine the bandwidth of reflectarray antennas.

5.1 Bandwidth Constraints in Reflectarray Antennas

5.1.1 Frequency Behavior of Element Phase Error

While reflectarrays mimic the traditional reflector antennas [1], there is an inherent fundamental difference between the two when it comes to system bandwidth [2]–[5]. A reflector antenna is essentially frequency‐independent, that is, it has an infinite bandwidth, and in practice the primary feed antenna is responsible for limiting the bandwidth of the reflector. On the other hand, a reflectarray suffers from bandwidth limitations due to the physical nature of its phasing elements and also the flat nature of its aperture. Both factors introduce phase errors as a function of frequency, which limit the bandwidth of reflectarray antennas.

For microstrip reflectarrays, the element itself has a bandwidth of typically only a few percent, ultimately ...