Results of Near Field Probe Scanning Tests for Ultralow Sidelobe Arrays

摘要

This report documents a unique Navy research program regarding fundamental measurement accuracy issues of near field antenna scanning. This work has accomplished both analytic studies and demonstration testing with very low sidelobe antennas. The program results have affirmed known relations between near field scanning errors and the resulting inaccuracies of the transformed far field sidelobe patterns. An existing planar near field scanner at the National Bureau of Standards in Boulder, Colorado has been modified to accept the large test antennas, and subsequently used for scanning tests with the AWACS phased array as well as a second experimental ultralow sidelobe slotted waveguide array. Results show that far field sidelobe accuracy is ultimately limited by uncontrollable random near field measurement error, multipath, and probe pattern directivity. A novel 'mainbeam nulling' probe has been shown to increase measurement accuracy of wide angle sidelobes by greatly minimizing the error gain in the coupling product during scanning. Classical probe correction post-processing is then necessary to recover the improved sidelobe pattern, but with degraded accuracy in mainbeam directions. The new probe radiates a fixed-direction null aligned with test antennas steered mainbeam. Catalogs of available data and results from unclassified antenna scanning tests are given in appendices. (Author)