Compact Dual-Frequency Dual-Circularly Polarized Feed for Ku-Band Satellite Communication Applications

This paper presents a compact dual-circularly polarized (dual-CP) feed operating in Ku transmitting (Tx) and receiving (Rx) bands for spaceborne flexible multi-beam reflector antennas. A novel approach based on a broadband septum circular polarizer (30.16% fractional bandwidth) is adopted in the dual-band dual-CP network, integrated with two compact corrugated diplexers and two 90° polarization-rotating structures, leading to a significant reduction in transverse size. A wideband profiled smooth-wall horn antenna is integrated with the proposed network, resulting in a feed with a transverse dimension of only $1.83{\lambda }_L\text{×}1.83{\lambda }_L$ @11.7 GHz. The feed offers left- and right-hand circular polarization (CP) separation and sub-band discrimination (Tx: 10.7–12.7 GHz and Rx: 14–14.5 GHz). The fabricated prototype exhibits return loss better than 17.6 dB and polarization ports isolation greater than 20.7 dB for both CPs in the two bands. It also achieves gains over 12.7 dBic and maintains axial ratios below 1.36 dB. This design ensures transverse compactness, bandwidth, and efficiency, facilitating the dense arrangement of elements within the feed array.