New concept for multibeam antennas based on two cascaded Ka-band transmit-array

Abstract

The paper presents a new two-beam per-feed approach for Ka-band multi spot-beam satellites. It is based on a dual-stacked transmit array (TA) arrangement, fed by a 3×3 standard waveguide array. The TAs are co-designed so that the first performs a beam collimation and tilting; whereas the second splits the incoming beam into two orthogonal circular polarizations, with symmetrical output angles relative to the incident angle. Therefore, the number of feeds is half the number of output beams, and the linearly polarized feed reduces significantly the antenna complexity. As a proof-of-concept, we design an antenna for the 30 GHz up-link band. The focal length of the first TA is 50 mm, and the aperture size of both TAs is 196×148 mm. A new type of phase correction, the multifocal approach, is used to minimize aberrations for all beams, which would be otherwise impossible with such low F/D. Using fullwave simulations, we confirm that the 18 beams present low SLL (~15 dB), pure circular polarization and good crossover (~3 dB) with gains between 21 and 22 dBi.