Grating Lobe Suppression in Ultrawideband Circularly Polarized Planar Array Based on ${\text {2}}\times {\text {2}}$ Irregular Sequential Rotated Subarray (ISRS)

This letter proposes a novel technique to produce desired circularly polarized (CP) pencil beams at entire working frequency band for ultrawideband (UWB) planar array while suppressing grating lobes in pencil beams at high-frequency band. The approach is based on a ${\text {2}}\times {\text {2}}$ irregular sequential rotated subarray (ISRS) configuration, using UWB linearly polarized elements. The synthesis procedure involves optimizing initial element rotation angle of each ISRS, while ensuring that the rotation interval of $\pi /2$ is still maintained between neighboring elements of each subarray. The phase term applied to the array elements is determined by the contribution of the phase associated with rotation. The proposed technique suppresses grating lobes in the obtained patterns at high-frequency band more effectively than the sequential rotation technique (SRT) while maintaining a simple sequential phase feeding network compared with the random SRT. Finally, one typical case of synthesizing pencil beam with a planar rotated Vivaldi array is presented to confirm the benefits of the proposed technique.