Narrow beam forming method for high frequency radar based on oblique projection operator

Spatial filtering is a valid approach to distinguish targets and suppress interferences. Conventional beam forming method relies on the increase of array aperture to form narrower beam. To improve the azimuth resolution without increasing the array aperture, a novel narrow beam forming method is proposed. By using zero phase-shift and deep nulls in the interference directions of oblique projection, multiple parallel spatial filters are constructed to suppress the interferences within the conventional beam. Therefore, the nulls are formed around beam direction and a narrower beam can be obtained by composing all the filter outputs. Compared with the traditional beam forming method, the method proposed is able to reduce the beam width significantly and improves the side lobe suppression ratio simultaneously. Especially, a narrower beam can still be formed when the array aperture is small. Experimental results of range-Doppler spectrum of high frequency radar demonstrate that, this narrow beam forming method can realize supper resolution of the target within the wide beam, and suppress the ionospheric clutter beyond the narrow beam formed, which achieve interference suppression within conventional beam and improved azimuth resolution of high frequency radar.