Compact Shared-Aperture Dual-Band Dual-Circularly-Polarized Waveguide Antenna Array Operating at K/Ka-Band

In this article, a compact shared-aperture dual-band dual-circularly polarized waveguide antenna array is presented to achieve high gain and wide bandwidth in full-duplex satellite communication at K/Ka-band. The designed antenna array can simultaneously operate at 20 GHz band with right-hand circular polarization (RHCP) radiation and 30 GHz band with left-hand circular polarization (LHCP) radiation. The array is composed of circular polarization (CP) waveguide antenna elements and full-corporate feed networks. The ridged spectrum polarizer is inserted in the square waveguide to form CP radiation in a stepped waveguide antenna element. The sequential rotation technique is adopted in feed networks to further improve CP axial ratio (AR) performance and bandwidth. The prototype of the proposed 4 $\times4$ antenna array is fabricated and measured for demonstration. Experimental results show that the overlapped bandwidth in terms of reflection coefficients less than -10 dB and AR lower than 2 dB is 18-22 GHz for RHCP radiation in K-band, and the corresponding bandwidth for LHCP radiation in Ka-band is 28-32 GHz. The measured cross-polarization levels are better than 25.82 dB at 20 GHz and 20.25 dB at 30 GHz, and the measured peak gains at K/Ka-band are 23.94 and 26.87 dBic, respectively.