Compact broadband circular polariser based on two-layer frequency-selective surfaces

A compact two-layer frequency-selective surface is presented to design circular polarisers for broadband applications. By optimising the parameters of the semi-circle metal strip element, an excellent simulated bandwidth of axial ratio (AR) (lower than 3 dB) is achieved from 10.02 to 11.09 GHz, while the amplitude of the transmission coefficient is higher than 0.8. Furthermore, the polariser unit cell is less sensitive to the range of oblique incidence angles. To verify the proposed design, an X-band circular polariser prototype is fabricated and measured. The results show that excellent AR performance can be achieved; the measured AR of the transmission wave is lower than 3 dB in the band from 9 to 12 GHz.