vector network analyzer

A vector network analyzer (VNA) is a type of test instrument used to measure important network parameters of RF and microwave components and networks.

A VNA usually consists of one or more signal generators, e.g., one for transmission measurement (or "forward measurement") and one for reflection measurement (or "backward measurement"), and one or more receivers that detect the amplitude and phase of the signals. Two built-in signal sources are of interest for amplifier intermodulation tests, for example, where two different frequencies are required for the test. For other measurements, one source can also provide the RF signal and the other the LO signal.

All VNAs apply a known stimulus signal to the device under test (DUT) and measure the response. By measuring the DUT's response at different frequencies and comparing it to the known stimulus, the VNA can determine the DUT's amplitude and phase characteristics, such as its gain, return loss, and transmission/reflection coefficients. This information can be used for the design, optimization, and troubleshooting of RF and microwave circuits and systems.

In a vector network analyzer, the DUT, such as an assembly or electrical gate, is measured over frequency rather than over time as in a conventional TDR.

For example, the assembly being measured can be fed a series of sine waves so that the signal changes that occur can be detected by the receiver in the network analyzer. This is done by determining the vector ratio between the incident and reflected voltages, sweeping the frequency of the sinusoidal waveform to determine the response of the device under test as a function of frequency. Thus, it is a relative measurement of transmitted and received signals. In particular, VNAs can also capture amplitude and phase as complex quantities and thus express scattering parameters (S-parameters) in complex-valued terms.

The acquired reflection and transmission data are presented by means of displays in such a way that the information can be interpreted in a user-friendly manner. Many RF network analyzers, therefore, offer features such as linear and logarithmic formats, sweeps, polar plots, Smith charts, etc. Trace markers, limit lines and pass/fail criteria can also be added.

Since VNAs have a wider dynamic range compared to TDR oscilloscopes, they can be used for more accurate measurements. In VNA-based time domain analysis, temporal signals are decomposed into their frequency components so that the signal can be reconstructed from the sum of these frequency components. Data measurements with VNAs are considered very stable, accurate, and versatile.

‍