Experimental results for adaptive radar imaging in a wide angular sector

We investigate experimentally an adaptive imaging approach, namely that of a synthetic wideband, stepped CW transmitter and a multichannel adaptive array for receiving backscattered energy from short range objects in a full +/-90 degree field of view. The method is a hybrid one, using conventional Fourier processing for range and is adaptive in angle. The 12-element linear array that was constructed is able to form an image in range and angle without Doppler information, and was tested with targets embedded in natural background clutter. The results show how background clutter affects the angular resolution of the array due to the increase in rank of the signal-plus-clutter covariance matrix, whereas at the same time the rank of this matrix is reduced for closely spaced scatterers due to signal coherence. In addition to investigating some known angular enhancement methods, we propose a method to enhance angular resolution in the presence of clutter by a projection, which seeks to reduce the received signal to a lower rank approximation, without using eigendecomposition, thus having an implementation advantage. This method allows more control over the angular resolution and the background clutter level. Computer simulations as well as the experimental results are presented.