Dual-Polarized Patch Excited Cup Antenna Array for Digital Beam-Forming Radar in Remote Sensing

Abstract

In the frame of an internal large-scale investment project, a ground-based radar working in X-band with 32 receive channels and real-time processing capabilities was built. Final purpose of the system is to investigate new radar technologies for future Synthetic Aperture Radar (SAR) satellites using Digital Beam-Forming (DBF) techniques. One focus of the project is on the exclusively developed antenna: A reflector antenna in offset geometry and a feed array with 4 x 32 dual-polarized elements. While typical radar requirements and the later space-applicability are in foreground, a major challenge is the feed design to provide DBF capability. Thus, a new antenna element for the feed array is developed, which overcomes fundamental limitations of state-of-the-art radar antennas. The invented Patch Excited Cup (PEC) antenna consists of a fully metallic body of size 0.6 x lambda (2.0 cm), which provides a high isolation to neighboring elements. In the center of the quadratic-shaped body there is a large drilling, which is denoted as “cup”. In the center of this cup a pin holds two metallic dishes, which serve as radiators. At the backside of the PEC two microstrip ring-hybrid couplers are used to feed the two orthogonal polarizations fully equal to provide symmetrical radiation patterns. During manufacturing and implementation, even new technologies and materials were successfully tested, like Ticer film resistors. The measurements of the antenna prototype in the anechoic chamber fully agree with the simulation results. We achieved a bandwidth of 9.1 - 10.5 GHz, a gain of 6.4 dBi and identical radiation pattern in E- and H-plane with 70° half-power beam-width. The cross-pol suppression within the main-lobe was higher than 26 dB and the element-to-element isolation better than 30 dB. Up to now even the complete reflector feed array with 4 x 32 elements was assembled and measured in the anechoic chamber. In future, the dual-purpose option of the antenna array for direct illumination (planar antenna) and for assembly as feed of the offset reflector antenna enables a wide range of research and applications.