Free-Space Phased-Array Characterization and Calibration Using Code-Modulated Embedded Test
A phased-array self-test technique called code-modulated embedded test (CoMET) is used for free-space characterization and calibration of phased-array transceivers packaged with antennas. Orthogonal two-bit modulation is applied to all phase shifters to allow for parallel extraction of gain and phase of array elements using a simple power detector. Our array uses two commercially-available beamformers and a patch antenna array. At 10 GHz, CoMET-extracted gain, phase, and phase offset are accurate to within 0.4 dB and 4° compared to network analyzer measurements. CoMET is then used within a calibration-loop to equalize elemental gain and phase across the array for 7-bit phase resolution. After calibration, the maximum gain and phase offsets between elements are reduced from 3.5 dB and 70° to 1.1 dB and ~0°. Free-space beam patterns after calibration show significant improvement.