Group delay (GD) is a critical parameter in satellite payloads and radar systems, directly impacting overall system performance. Although several antenna group delay measurement methods exist, most overlook the challenges posed by frequency conversion chains commonly used in these applications. This paper introduces a method to accurately address this issue by implementing an additional calibration step of the vector network analyzer (VNA) using a harmonic phase reference (HPR). The method is validated through far-field measurements on a device equipped with a mixer.