Dual Circularly Polarized Millimeter-Wave Transmitarray

This communication reports the dual circularly polarized high-aperture-efficiency transmitarrays (Tas) capable of forming patterns with two independent beams for the right-hand circularly-polarized wave (RHCPW) and left-hand circularly-polarized wave (LHCPW) at the same frequency. The five-layer TA elements contain a ring-slot resonator loaded by interdigital capacitors in each layer. The TA element was optimized as a three-bit phase shifter that adds two independent phase shifts to the transmitted RHCPW and LHCPW. The geometry of the TA element was validated by designing two 500-element TAs. At 36.5 GHz, these two TAs form RHCP beams in the directions
$(\theta =20^{\circ}, \phi =0^{\circ})$
and
$(\theta =40^{\circ}, \phi =0^{\circ})$
, respectively, and the LHCP beams point in the direction
$(\theta =0^{\circ}, \phi =0^{\circ})$
in both TAs. These two TAs were fabricated and tested. For the first TA, the measured gains were 27.7 and 27.6 dBi for the RHCP and LHCP radiation patterns, respectively, with overall aperture efficiencies
$\eta _{s}$
of 0.46 and 0.45. The second TA demonstrated the measured gains of 27.0 and 28.5 dBi for the RHCPW and LHCPW, respectively, with
$\eta _{s}$
equal to 0.39 and 0.55. The measured cross-polarization levels in the direction of pattern maximums were −21.1, −24.4 dB for the first TA, and −15.0, −31.2 dB for the second TA, considering RHCPW and LHCPW beams, respectively.