In-Situ Calibration of Plane Wave Generator in an Aperture-Limited Multi-Probe Compact Setup

A plane wave generator (PWG), capable of approximating a plane wave condition for over-the-air (OTA) antenna testing with a short measurement distance, has attracted huge interest from both academia and industry in recent years. Variations in the PWG radio frequency (RF) chains due to active RF components would alter the optimized complex excitation coefficients of PWG, which can inevitably deteriorate the PWG quiet zone (QZ) performance. Therefore, regular calibration of a PWG is essential to maintain optimal PWG QZ performance. However, plane wave condition, which is typically required for PWG array calibration, is difficult to attain in practical PWG deployment scenarios. To address this challenge, a novel scheme is proposed for in-situ calibration of the PWG. The basic idea is to employ a small multi-probe system (i.e., with its aperture smaller than that of the PWG) located within the PWG QZ in the compact setup to emulate an ”equivalent probe” much further away from the PWG. The proposed solution is validated in a practical anechoic chamber setup, where a 3 × 3 multi-probe system (with a small aperture of 0.5 m ×0.5 m) is employed to calibrate a 14 × 9 PWG (of size 1.0 m ×1.124 m) at 2.6 GHz with 0.5 m measurement distance. A good array calibration accuracy is achieved, with a peak-to-peak amplitude error of up to 1.5 dB and phase error of up to 11.2°, even in the presence of probe placement errors in practical deployment scenarios. The proposed multi-probe system solution along with the probe placement error correction scheme is experimentally demonstrated to be highly effective in mitigating non-idealities in practical measurements, making the solution highly cost-effective, fast, and accurate for in-situ PWG calibration.