Performance of a broadband ring element reflectarray

The scattering from a grounded array of double layer ring and concentric ring elements is compared at X-band. For both periodic arrays, it is shown that the reflection phase variation with ring diameter is controlled by the difference in the centre resonant frequency of the two elements. This parameter can be selected to give a linear phase versus ring size plot with a small gradient which is required for broadband reflectarray antenna design applications. The TLM method was used as a computer simulation tool and the results were compared with waveguide simulator measurements to demonstrate the validity of the predictions.