Abstract: The rectangular close-packed antenna array is studied in the paper. The far-field directional diagram of the array is emulated, which indicates it is possible to get highly active combination based on the close-packed antenna array and the main beam can be got. Then the impact of element separation and initial phase of the element on spatial power combining of the antenna array is analysed, and the results show that the smaller the element separation is, the less the grating lobes becomes, and the wider the main beam is, the shorter the critical distance becomes when the main beam can be obtained. When the distance between the target and the arrays exceeds the critical distance, the synthesis efficiency increases with the decrease of the phase difference of the arrays. But the arrays cant obtain certain main beam when the distribution range of initial phase of the arrays exceeds /2. So the above factors should be considered in array design.