Millimetre-wave imaging with reduced number of degrees of freedom in array signal processing: concepts for enhanced angular resolution

This paper deals with millimetre-wave imaging systems based on linear receiving arrays and is focused on the issue of angular resolution and coverage for arrays where the number M of ports is smaller than the number N of elements due to forming of subarrays. For a wide angular coverage a trade-off between a narrow beam width and a high side-lobe suppression is shown to occur which requires proper synthesis of the subarray pattern. Two concepts for an enhanced angular resolution are presented. The first uses a combination of a frequency dependent distribution network (frequency scanning) with array signal processing to enhance angular resolution by cost of a reduced range resolution. The second approach takes advantage of relative movements to enhance angular resolution via a combined angular and temporal (Doppler) processing