A Dual-Channel Linear-to-Circular Polarization Conversion Transmitarray With Independent Wavefront Control Capability

In this article, the design and proof-of-concept demonstration of a dual-channel linearly polarized (LP) to circularly polarized (CP) conversion transmitarray are reported, which possesses the capability of independent beamforming for each channel. The fixed receiving patch and rotatable transmitting patch of the employed unit cell are connected by introducing two orthogonal signal paths with a phase difference of 90
$^{\circ}$
. Hence, the dual orthogonal LP incident waves from feeds can be effectively converted to dual CP radiation, therefore creating two independent LP-to-CP conversion channels. Moreover, based on a hybrid compensation strategy of propagation and geometric phase, the unit cell can provide independent phase control for the two channels through the cooperative control of the length of the two signal paths and the rotation angle of the transmitting patch. To demonstrate the proposed methodology, a 2
$\times$
2 bit dual CP transmitarray with a designed dual LP horn feed, featuring different beam directions, is developed by utilizing the independent dual-channel phase shifting unit cell. A prototype of the integrated transmitarray is fabricated and characterized, exhibiting a good agreement between the simulation and the measurement. The measured gain at the center frequency of 20 GHz for the two channels is 23.6 and 23.1 dBic, and the joint bandwidth of 3-dB axial ratio (AR) and 3-dB gain bandwidth is wider than 20%. With advantages of independent controllability, good CP performance, and stable radiation pattern, the proposed wideband dual-channel CP transmitarray would be an attractive candidate for wireless and satellite communication systems.