Features Overview of RF and Microwave VNA Test Cables for Vector Network Analyze

A vector network analyzer is used to achieve accurate measurements, and the instrument needs to support calibration. Usually measurement requires a set of test equipment, including a network divider, a set of calibration tools, and one or more VNA Test Cables and adapters. The calibration process uses vector error correction techniques to characterize the error terms using known standards. Therefore these errors can be eliminated by actual measurement. The process of eliminating these errors requires that the errors and the quality of the measurements be calibrated in the vector direction. After calibration, high-precision measurements can be achieved. Any changes may reduce measurement accuracy. Usually temperature changes, bending and movement of the VNA Test Cable, vibration and drift can affect the measurement accuracy. This article will focus on the VNA Test Cable. The article will clarify why and how bending and movement of the VNA Test Cable affects measurement accuracy, and how to define a VNA Test Cable to evaluate its effect on accuracy.

Through vector error correction for the entire measurement setup, the transmission and reflection characteristics of the VNA Test Cable can be algorithmically eliminated in magnitude and phase. Subsequent movements of the VNA Test Cable cause small changes in internal dimensions, stressing of insulating materials, changes in contact resistance and shielding, all of which contribute to slight changes in transmission and reflection characteristics. As a result, the vector error correction is no longer effective, resulting in reduced measurement accuracy.

                                                           
VNA Test Cable details

The VNA Test Cable designed for high-end network points is called a test port cable. They are designed to move and bend frequently when docked to a specific test setup, and are often armored to prevent damage from mechanical stress. In addition to hard specifications, "Typical Values" are often mentioned, sometimes graded over frequency bands. Please note that these specifications will vary with the length of the VNA Test Cable, but are valid for different bending states. "Insertion Loss Stability", "Fading Stability" and "Amplitude Stability" mean the same thing.

The VNA Test Cable has a significant impact on the phase in the full frequency band, and has a significant impact on the amplitude in the low frequency part. For both measurement cables, the amplitudes at intermediate and high frequencies are affected similarly by the mesh and measurement cables. Reflection measurements in the VNA Test Cable are also affected. Often, changes in reflection amplitudes need to be evaluated as well as return loss behavior. We do not discuss the detailed comparisons between network split uncertainty and VNA Test Cable effects here. In routine test tasks, based on the acceptable measurement uncertainty, it is necessary to evaluate the impact of a single VNA Test Cable more specifically, such as how to reduce the overall test uncertainty under frequency range and bending conditions.