Reflectarray Antennas

7Broadband and Multiband Reflectarray Antennas

The reflectarray is inherently a narrowband antenna [1], [2]. With a typical design, the bandwidth of a reflectarray antenna is only a few percent, depending on the element selection, the size of its aperture, and f/D ratio. This basic limitation has stimulated engineers to find solutions to improve the bandwidth of reflectarrays and various broadband techniques have been developed over the years. Moreover, techniques have been proposed to provide coverage to two or more widely separated frequencies. In this chapter, we will present the design methodologies that have been developed for broadband and multiband reflectarrays.

7.1 Broadband Reflectarray Design Topologies

7.1.1 Multilayer Multi‐Resonance Elements

As discussed in Chapter 2, a simple and practical way to obtain a progressive phase shift of the reflected field is by varying the resonant length of the patches [3], [4]. This technique allows simple manufacturing, and it produces lower cross‐polarization levels than the stubs of different lengths attached to the radiating patches. To design a reflectarray, the phase of the reflected wave should have a progressive variation over the whole surface, essentially implying that a full phase cycle should be used for the reflection coefficient. The phase range obtained by varying the resonant length of a patch depends on the substrate thickness, that is, the smaller the thickness, the greater the phase range. For a thickness ...