A least squares approach for radar array adaptive nulling

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Electrical Engineering and Computer Science


Tapan Sarkar


early warning, interference rejection, electrical engineering

Subject Categories

Electrical and Computer Engineering


Space-time adaptive processing (STAP) is being investigated for interference rejection for airborne early warning radars. For over twenty years the focus of STAP has been on a statistical approach that uses secondary or training data to develop an understanding of the interference environment. This approach requires that sufficient secondary data be available that is statistically homogeneous with the radar range cell under test. In many situations it is difficult to meet these secondary data requirements. Limited multichannel airborne data is available but what does exist indicates that clutter can often be nonhomogeneous.

A direct approach to interference rejection has been developed that employs data only from the range cell of interest. This approach would avoid the concerns about homogeneity of secondary data. However in this direct approach the target, if one exists, is included in the data set that is being used to determine the adaptive weights. In many nonradar applications the desired signal is arriving from an exactly known direction and the gain can be maintained in that direction by a look-direction constraint while adaptive nulls are placed in the directions of the interfering sources. These nulls are established by canceling equations from which the desired signal is removed. This can be done because the phase progression of the desired signal is exactly known. For radars, however, the desired signal can arrive over a finite angle extent. All target returns in the transmit mainbeam must be processed for detection.

In this research a multiple constraint approach to interference rejection is developed that prevents nulling in the target direction and overcomes the effects of residual signal in the canceling equations. This algorithm is summarized in a multiple step approach that insures that the interference can be rejected and the target detected for various signal strengths and target locations within the mainbeam.


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