Monopulse elevation discrimination experiments in low-angle multipath

Tracking a low-altitude target in elevation is difficult when both direct and reflected radar returns originate within the main beam of the interrogating radar. In such conditions, a conventional monopulse radar is subjected to increased angle noise and bias error in elevation. This is a long-standing, unsolved (in a practical sense) problem in low-elevation target tracking. A novel application of a target extent estimator ("C-2") has recently been shown theoretically capable of mitigating both specular and diffuse multipath interference in low-elevation tracking situations. Under Navy Phase II SBIR funding, ORINCON, Signalogic and TRW have collaboratively investigated the application of this technology by processing data collected during X-band experiments on real targets in low-level flight at NAWCWPNS, Point Mugu in early 1998. We describe the design and performance of these flight test experiments and summarize the salient off-line signal processing results, which demonstrated reliable elevation tracking in the horizon region with rms errors typically on the order of one-twentieth of a beamwidth. We conclude with a discussion of areas for future research and development of this technology.