Large-Scale Planar Array Near-Field Calibration Based on Plane Wave Spectrum Maclaurin Expansion

This communication introduces a novel near-field calibration method for large-scale planar arrays. A novel signal model is developed by representing the plane wave spectrum (PWS) corresponding to the measured signals as a Maclaurin series expansion. By performing the Fourier transform of each polynomial term in this expansion, the measured signals can be expressed as a linear combination of the derivatives of the free-space scalar Green's function. The initial excitations and Maclaurin coefficients are jointly estimated through iterative minimization of an evaluation function, which is defined by measuring the difference between the measured signals and the virtual signals computed using the proposed signal model. An alternating optimization strategy is employed to ensure fast and efficient convergence of the minimization process. A 6×9 planar array composed of rectangular open-ended open waveguides was calibrated at a measurement distance of 0.5 m using the proposed method, achieving a calibration error range of ±0.58 dB and ±4.9°. The calibration was conducted using probe measurements over approximately one-quarter of the AUT aperture, with a 3 × 3 uniformly spaced rectangular sampling grid within this scanning region. The obtained results validate the effectiveness of the proposed calibration method.