A Circularly-Polarized Multi-Beam Magneto-Electric Dipole Transmitarray With Linearly-Polarized Feeds for Millimeter-Wave Applications

This communication presents the design of a wideband circularly polarized (CP) multibeam transmitarray with a cluster of linearly polarized (LP) feeds for millimeter-wave applications. A novel receiving/transmitting (Tx) unit cell, composed of one LP and one CP magnetoelectric (ME) dipoles, is designed with capability of converting the incident wave from LP source to CP radiation and enabling to provide a full 360 degrees geometric phase coverage by rotating the CP element. The geometric phase compensation is realized by setting the space-dependent rotation angle for the Tx array such that it exhibits a wide frequency response in producing directive CP beam radiation with improved axial ratio (AR) performance. Moreover, a bifocal strategy is employed in the design of the multibeam transmitarray to achieve a small scanning loss. To verify our proposed methodology, a prototype of the bifocal multibeam transmitarray with seven LP ME dipole source radiators is fabricated and measured. The obtained results show that the seven beams can cover a range of +/- 33 degrees with a peak gain of 21.5 dBic and a scanning loss of 2 dB. Meanwhile, the overlapped bandwidth for the reflection coefficient vertical bar(S-11)vertical bar <= -10 dB), the 3 dB AR, and the half-power gain is around 33.3% (23-32 GHz).