Scan Limitations of Open-ended Ridged Waveguide Phased Array Antennas for Satellite Communication

Open-ended ridged waveguide phased array antennas (PAAs) are promising candidates for future low Earth orbit satellite communications. This paper analyzes the scan limitations regarding the active reflection coefficient (ARC) and the axial ratio (AR) of circular and hexagonal waveguide elements with three and six ridges for Ka-band satellite downlink applications. For the hexagonal waveguide element with six ridges, it is shown that the degradation of the ARC and the AR at high scan angles and frequencies can be related to the onset of higher Floquet modes, resulting in single-mode scan blindness associated with one of the two orthogonal fundamental modes of the waveguide that generate the circular polarization. Reducing the element periodicity to delay the onset of higher-order Floquet modes overcomes the single-mode scan blindness and meets the Ka-band satellite downlink AR requirements.