An On-the-Fly Calibration Method for Air/Spaceborne Active Electronically Scanned Antenna Arrays

Large-scanned antenna arrays need to be periodically calibrated to correct for errors in excitation amplitude and phase, which degrade performance. The ability to adjust complex excitations to correct for these errors necessitates an accurate method to determine the errors that are present. Commonplace approaches require far-field calibration targets or sensors, additional hardware such as near-field sensors or self-sampling circuitry, or are limited to specific array configurations. These requirements are difficult to meet for arrays mounted on aircraft and spacecraft that cannot be easily accessed during operation or operate under transient conditions. If operating conditions change quickly, fewer types of calibrations are feasible. This could be due to temperature changes, aging and fluctuation of the electronic components, or deformation of the array structure. In prior work, we show how distributed targets can be used to determine changes in element-to-element channel imbalances in pairs of receiver antennas using the underlying terrain through synthetic aperture radar (SAR) imaging. This work reports on the extension of the procedure to the calibration of an advanced wideband 16-element active electronically scanned array (AESA) with transmit and receive capabilities that we fabricated as a testbed. Several important scenarios are investigated which show that the proposed method is feasible and robust to complications present in airborne environments. These scenarios include calibration of both transmit and receive array elements, over a range of signal-to-noise ratios (SNRs), and with distortions to the array structure that result in uncertainties in element positions.