A Novel Near-Field Calibration Method for Linear Array Based on Plane Wave Expansion

This article presents a novel near-field calibration method for linear arrays based on plane wave expansion. The proposed method enables the calibration of an antenna under test (AUT) with a compact measurement distance and a probe scanning aperture as small as 1/10 of the AUT aperture. The calibration measurement can be implemented by moving a probe antenna in a sparse grid along a line segment parallel to the AUT and collecting the AUT array element response. In the proposed method, an ideal virtual linear array is employed to model the AUT, where the virtual AUT possesses the same configuration as the AUT and consists of array elements with consistent radiation characteristics. The virtual AUT is determined by minimizing the difference between the response of the virtual and actual AUT, where the virtual AUT response can be constructed based on plane wave expansion. The least square (LS) method is applied to minimize the difference, while an optimization algorithm is employed to solve the radiation characteristics and the initial excitations of the virtual AUT. In the validation measurement, a nonuniform linear array (NULA) is calibrated in the near field using the proposed method with a probe scanning aperture of only 1/10 of the AUT aperture and a measurement distance of 4.33 wavelengths at 2.6 GHz. Based on the obtained results, +/- 0.41 dB in amplitude and +/- 4.7 degrees in phase calibration accuracy are achieved, respectively, demonstrating the effectiveness of the proposed method.