Group Delay (GD) is an important parameter in advanced antenna systems, especially for applications demanding high timing precision and signal fidelity, such as GNSS, satellite communications, and modern 5G networks. This work presents, for the first time, the validation of absolute GD measurements using spherical near-field Multi-Probe Array (MPA) systems, which enable rapid and accurate 3D antenna characterization. To achieve reliable absolute GD measurements, a GD substitution method is employed to correct for the GD introduced by the measurement system itself. This is accomplished by measuring a reference antenna with known GD under the same test conditions of the test antenna. The use of multi-purpose reference antennas is proposed to perform both gain and GD calibration simultaneously, simplifying the overall calibration workflow.
Experimental validation is carried out in the 5–6 GHz band using a variety of antenna types, including horn, dipole, and bicone antennas, demonstrating excellent agreement between measured and simulated GD values across both frequency and spatial domains. The results confirm the robustness and accuracy of the proposed methodology. Importantly, this study reinforces the capability of MPA systems not only for conventional amplitude-related metrics such as gain, radiation pattern and efficiency, but also for accurate characterization of phase-related quantities like the GD. This confirms MPA systems as versatile and powerful tools for comprehensive antenna performance evaluation.