Metallo-Dielectric Millimeter-Wave Huygens’ Quarter-Wave and Half-Wave Plates

A novel metallo-dielectric Huygens’ unit cell is proposed that can be designed to operate either as a quarter-wave plate (QWP) or as a half-wave plate (HWP). The unit cell is based on a single-layer perforated dielectric, with straight (nonmetallized) and 45° (metallized) elliptical holes. The novelty of the unit cell is its suitability for millimeter-wave implementation in printed-circuit board (PCB) fabrication due to the absence of metallic patterns of small line widths and gaps. As an example of their applicability, the wave plates are demonstrated in the near-field of 60-GHz band diffusion-bonded slot array antennas. The unit cell operating as a QWP is demonstrated in full-wave simulations and experimentally for linear-to-circular polarization conversion, whereby the combination of a linearly polarized antenna and the QWP produces a circularly polarized wave. Measurement results of the antenna and the QWP show
${\le }-10$
-dB reflection from 59 to 63 GHz (6.6%),
${\le }3$
-dB axial ratio from 59.5 to 61.5 GHz (3.3%), and an overall efficiency
${\ge }77\%$
from 59.5 to 61.5 GHz. The unit cell operating as a HWP is demonstrated in full-wave simulations for polarization rotation of the linear polarization (LP) antenna, and for changing the sense of rotation of a right-hand circular polarization (CP) antenna into left-hand CP.