Phased Array Fed Reflector (PAFR) antenna architectures for space-based sensors

Communication link and target ranges for satellite communications (SATCOM) and space-based sensors (e.g. radars) vary from approximately 400-1000 km for low earth orbits (LEO) to 35,800 km for geosynchronous orbits (GEO). At these long ranges, large antenna gains are required and most legacy systems use high gain reflectors with beams that are either fixed or mechanically steered. However, for some radio frequency (RF) sensor applications, mechanical beam scanning has inherent limitations. Direct Radiating phased Arrays (DRAs) can provide electronic scanning and/or multiple beams over a wide field of view (FOV). However, large DRAs are generally more complex and expensive than reflector antennas. Phased Array Fed Reflectors (PAFRs) offer intermediate performance by utilizing smaller (feed) arrays to provide electronic scanning over a limited FOV. Approximately ±5 to ±10 degrees of electronic scanning is typical for PAFRs, but this range depends on many factors. For LEO applications, the earth FOV is approximately ±55 degrees and this is well beyond the range of electronic scanning for PAFRs. However, for some LEO missions, a limited scan range is sufficient or the space vehicle design and operations can incorporate a combination of mechanical slewing and electronic scanning. In this paper, we review, compare and contrast various PAFR architectures that are widely applicable to a diverse set of space missions (both earth sensing and interplanetary). We then compare the RF performance of these architectures and describe key hardware design and implementation trades. Space-based PAFR designs are highly multi-disciplinary, so we also describe the various design/analysis methodologies and relevant technologies. Finally, we summarize two PAFR prototype architectures that have been demonstrated at Northrop Grumman.