In the real world, vector network analyzer (VNA) measurements in the field often present obstacles to obtaining accurate readings. In this article, we examine the effect of a long coaxial cable between the VNA and the device under test (DUT), and show the benefit of moving the VNA directly to the DUT.
VNA measurement errors are typically modeled with network flow graphs to depict errors due to internal VNA hardware and the effect of external cables and connectors. In the model, the VNA is assumed to be perfect, and all systemic, non-random errors are modeled by an error box between the perfect VNA and the DUT.