A Vector Network Analyzer (VNA) is a test instrument capable of emitting signals across a wide range of frequencies. The signal is measured as it leaves the VNA port, and any reflections that return to the port are also measured. The VNA can also measure a signal entering a separate port. If you need a simple starting point for understanding vector network analyzer basics, this is it.
This is what distinguishes a VNA from other test equipment: it can separate and measure signals traveling in both directions on a transmission line. Knowing how much signal passes through a Device Under Test (DUT) and how much is reflected back to the source allows complete characterization of the device. This information can help predict DUT performance when driven and loaded by any arbitrary complex impedance. Here we cover some VNA measurement applications.
Amplifiers
Vector Network Analyzers (VNAs) are extensively used in design and production testing for a large number of electronic devices. RF amplifiers can be characterized in terms of gain, input return loss, P1dB, output matching, and stability. These characteristics are important to verify when designing an amplifier in an RF system.Filters
Filters are an important part of most RF systems. A receiver designed to operate in a specific bandwidth will inevitably have a filter at the front to limit input to those frequencies. If the signal is mixed up or down to another frequency, a filter is required before the mixer to avoid ambiguous mixing at the image frequency.A VNA can measure the passband insertion loss of a filter, S21, and the return loss at the input, S11. It can also measure rejection bands, and VNAs from Copper Mountain Technologies have exceptional dynamic range that allows them to measure both the passband and deep rejection bands in a single measurement.
Control Systems and Satellites
Satellite systems operate at microwave to millimeter-wave frequencies. Up-converters and down-converters are commonly used to convert these high-frequency signals to a more manageable frequency for demodulation or to convert modulated lower-frequency signals to K or Ka-band frequencies. A Vector Network Analyzer (VNA) can perform offset frequency measurements. Sweep the low-frequency input of the up-converter and measure the output at the higher frequency. Conversion loss or gain can be measured directly. Similarly, the high frequency of a down-converter can be swept and the low-frequency output measured.The gain flatness of the frequency converter is usually very important, so this measurement is very useful. The ability to perform offset frequency measurements is a standard feature of all Copper Mountain Technologies VNAs except for the economical grade Compact Series Model M VNAs.
Cables and Waveguides
It is very common to use a Vector Network Analyzer (VNA) in RF cable production. Handheld 1-port portable VNAs are conveniently used to verify proper cable performance while still on the production machine. Feed lines to antennas can be evaluated using Time Domain mode to verify characteristic impedance along the distance and check for damage or moisture ingress.Waveguide transmission lines can be measured with an appropriate coaxial-to-waveguide adapter. As an example, the long run of waveguide from the radar to the transmit antenna on a naval vessel can be evaluated using the Time Domain function in much the same way as a cable feed line.
Antennas
An antenna must convert a signal on its feed line into radiated RF energy if the frequency is within the operating bandwidth. A reflection measurement is sufficient to evaluate an antenna's capability and health status. If there is high reflection, it is clear that little energy will be radiated. On the other hand, if reflection is low, it can be assumed that energy is being radiated. Return loss (S11) or voltage standing wave ratio (VSWR) are the commonly measured parameters.Material Measurement
Millimeter-wave Vector Network Analyzers (VNAs) can be used to perform material measurements. A sheet of material to be measured is placed in a frame between two antennas connected to a VNA. Two lenses focus the beam to transform circular wavefronts into plane waves. The dielectric properties of a material sheet can be measured this way. This can be important for evaluating a material used in a radome. The complex dielectric constant of the material can be calculated from these S-parameter measurements in air.Food and Beverage Industry
In the food industry, one could use a Vector Network Analyzer (VNA) to measure the dielectric properties of a liquid using a SPEAG probe in Switzerland. Time Domain function could be used to determine the liquid level in a sealed opaque container, and latent moisture contained in bread, muffins, or cupcakes could be evaluated with a simple reflection measurement.Agriculture
A Vector Network Analyzer (VNA) can be used to measure moisture in substances such as soil, grains, or wheat. Water has a very high dielectric constant, near 80, so its presence significantly increases the magnitude of RF reflections. A VNA could also be used to measure something like the ripeness of fruit or melons.Medicine
Microwave imaging is an exciting advancement in the field of medical imaging. This method is much safer than using ionizing X-ray radiation. For example, a Copper Mountain Technologies Vector Network Analyzer (VNA) is integrated into the MammoWave breast cancer detection imaging system from UBT.These are just a few examples of what can be measured using a vector network analyzer. For more information, visit our Technical Library or Applications page for more information on VNA testing in different industries.