Large-Scale Phased Array Calibration

One challenge in fielding large-scale phased array antennas is calibration of the antenna system, so that RF radiated beams can be accurately formed and steered. Here, we describe two new methods for calibrating large phased arrays, namely, the mobile Fourier gauge (MFG) and satellite-based calibration (SatCal) that permit rapid calibration of large phased arrays on site and that remove the need for expensive nearfield facility testing that limits the size of the array sections that can be RF aligned. The MFG utilizes a known short RF line source that can be sequentially moved across the array using an existing crane; RF coupling measurements between this RF line source and the array elements made at different RF line source positions are vector summed, so as to form a known virtual RF line source that stretches the length of the array. A second independent method, SatCal, is presented that uses reflections from orbiting satellites to calibrate the array, either at the subarray or radiating element level. These calibration methods have been demonstrated on a large S-band phased array and have resulted in array calibrations equivalent to within 5°, 0.7 dB rms (element level), or 4°, 0.6 dB rms (subarray level).