Combining Pancharatnam-Berry Phase and Spherical Conformal Transmitarray for High-Efficiency Beam Focusing

In this article, a Pancharatnam-Berry (PB) phase-based spherical conformal transmitarray (SCTA) is proposed. With the aim of achieving high aperture efficiency (AE), the Goldberg polyhedron typology is introduced to realize spherical conformal aperture. In this manner, the issue of oblique incidence encountered in planar and cylindrical conformal transmitarray antennas (TAs) is addressed, thereby obviating the associated phase error and amplitude attenuation. Moreover, a significant reduction in both total volume and effective aperture area is achieved for the SCTA when compared to its planar TA counterparts. Furthermore, a single-layered PB phase-based unit cell is designed to realize precise transmission phase control with 360° phase coverage by rotating the unit cell. Detailed derivations and analyses are conducted to acquire the transmission phases and the rotation angles of all the unit cells. Consequently, a high-efficiency PB-SCTA antenna, comprising 88 unit cells, has been designed within a hemispherical structure with a radius of <inline-formula> <tex-math notation="LaTeX">${2.38\lambda _{0}}$ </tex-math></inline-formula>, the PB-SCTA is full-wave simulated, manufactured, and measured. The proposed PB-SCTA, operating at 14.25 GHz, has achieved a high gain of 20.03 dB, a high AE of 60.1%, and salient front-to-back ratio (FBR), sidelobe level (SLL), and cross-polarization level (XPL) performances. Comparisons are carried out between the proposed PB-SCTA and various state-of-the-art TAs to demonstrate the superiority of the proposed design in terms of structural compactness, unit cell complexity, and radiation performance.