Broadband Two Layers 1-Bit Metal-Only Transmitarray with Polarization Conversion Technique

A novel broadband two layers 1-bit metal-only transmitarray based on multi-frequency phase distribution synthesis is introduced in this paper. The proposed element for the antenna is composed of two identical double C-shaped slots etched on two metallic top and bottom plates with 90 º differences between their orientations to guarantee the polarization conversion for the transmitted wave. The phase state of the transmitted wave is simply varied by 180
^º
by only rotating the bottom metallic layer equal to 180
^º
. Four posts are placed between the two metallic screens to not only further improve the frequency bandwidth behavior of the element but also enhance the robustness of the structure mechanically. The simulation results showed that the x-polarized transmitted wave has an amplitude larger than 0.9 from 12.5 GHz to 17.3 GHz when the y-polarized wave is illuminated to the structure. To achieve a flat gain response within the band, the optimum phase distribution of the array is obtained using a multi-frequency synthesis method based on reference phase optimization for different frequencies. To this end, the variance of the gain level of the antenna is considered as the cost function in the optimization algorithm. A 17.5 cmx 17.5 cm (25x25 element) transmitarray is designed and simulated and the results showed that the pattern has a flat gain response and the 1-dB gain bandwidth is 13.5 GHz-18 GHz (28.57
^%
).