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Design of Two-dimensional Millimeter Wave Virtual Array Based on Sparse MIMO Array

This paper presents a two-dimensional millimeter wave virtual array based on the concept of sparse multiple-input multiple-output (MIMO) array. The array antenna is designed for advanced W-band real-time imaging applications. Such systems have an ability to obtain high resolution images of the target under test. A large-scale array aperture with a narrow beam is required for this kind of systems. This results in complicated RF front end and very high cost. As an alternative, the utilization of MIMO array concept for the virtual array is a feasible solution. This design approach can reduce the number of antenna elements significantly while keeping the same level of array pattern. In our study, the virtual array is consisted of 12 transmitting channels and 16 receiving channels. Each channels is connected a 16-element series-fed microstrip patches. By using the MIMO design approach, a large-scale array with 48 × 32 elements is obtained. The Simulation results show that the series-fed microstrip patches achieves good impedance match (VSWR ≤ 2) from 76 GHz to 81 GHz. The zero points of the receiving array pattern are matched with the grating lobes resulting from the transmitting array and vice versa. So there is no grating lobe in the two-way array pattern. It makes the virtual array has the same pattern as the physical large-scale array. Simulation results show that beamwidths of the virtual array are 2.1° and 2.5° in horizontal and vertical planes, respectively.