Radar multifrequency measurement of elevation angles of low-altitude targets above the sea using the ROOT-MUSIC method

Subject and Purpose. The article is devoted to the problem of precision radar measurements of target position data when a low-altitude target is above a rough sea. In these circumstances, the thermal noise of the radar receiver and the sea clutter are picked up by the radar antenna in parallel with the target useful signal and are factors affecting measurement accuracy. A particular challenge is the target elevation measurement.

Methods and Methodology. A number of methods are known to significantly improve the measurement accuracy. The root-MUSIC method is among them, and the present paper examines a possibility to improve its performance due to multi-frequency measurements. The study is conducted by means of computer simulation using three-frequency X-band radar at the typical conditions: the path length is 2000 m, the antenna array height above the sea level is 12 m, the target angle of altitude is 0.2 to 0.5°. The multi-frequency measurement performance is evaluated by comparison with the single-frequency results obtained in the identical conditions with various sea clutter levels and different thermal noise figures in radar reception channels.

Results. A preliminary analysis has been given to the measurement error distribution during conventional single-frequency measurements through different phases of the interference field structure of the received signal. It has proved the multi-frequency mode of operation as a means for the error reduction in target elevation measurements. The measurement error dependences on target elevation angles were studied with various real-valued frequency separations. Based on three particular estimates at each of the operating frequencies, an algorithm of the generalized estimation of the elevation angle has been developed and tested. An operating frequency separation to keep measuring errors to a minimum has been justified.

Conclusion. It has been shown that a simultaneous use of three operating frequencies can reduce measurement errors by no less than 20...40% compared with the operation at a single frequency.