K-/Ka-Band Planar Shared-Aperture Beam-Scanning Array Antenna for Simultaneous Transmitting and Receiving Low Earth Orbit Satellite Communication Terminal

Abstract

A planar shared-aperture beam-scanning array antenna for simultaneous transmitting and receiving (STAR) satellite communication is proposed. The antenna operates in dual working bands with right-handed circular polarization (RHCP) from 17.7 to 21.2 GHz and left-handed circular polarization (LHCP) from 27.5 to 31.0 GHz. For the K-/Ka-band shared-aperture beam-scanning array antenna, the main challenge is to simultaneously achieve a wide beam scanning range, low profile and high cross-band isolation. Compared to high-profile end-fire duplexing or filtering antennas, planar laminated antennas have a stronger coupling between two elements operated at different frequency bands. In this design, two embedded two-stage filters are proposed and integrated into the dual-band feeders. The minimum spacing between the elements is 1/4 wavelength, and both in-band wideband impedance matching and cross-band filtering are performed simultaneously. Firstly, two square lattices with a 45° rotation angle between them and a non-stacked topology are employed in the design of uniform arrays for both bands. This design is better suited for this filtering array. Secondly, to improve CP performance during the beam scanning, the Ka-band induced current on the K-band radiator should be suppressed. The rotary feed phase and the segmented patch are used to suppress the induced current and produce the reverse induced current in the small and large beam scanning area respectively. Finally, the equivalent circuits and chain matrices are used to design the filtering feeders. As a result, the dual cross-band isolations increase to 38 dB and 41 dB. The total profile is less than 3.2 mm, much smaller than the existing K-/Ka-band filtering antenna’s profile of 10 mm, and the proposed design also has a wide operating bandwidth and a large beam scanning range of ±60°.