RF network analyzer basics tutorial
- a tutorial, information and overview about the basics of the RF network analyzer what is a network analyser and how to use them and including the vector network analyser, VNA and the large signal network analyser, LSNA.
One item of test equipment that is widely used by RF design laboratories is the RF network analyzer. Not to be confused with network analysers used for analysing data networks, the RF network analyser is used for characterising or measuring the response of devices at RF or even microwave frequencies.
By measuring the response of a device or network using an RF network analyzer, it is possible to characterise it and in this way understand how it works within the RF circuit for which it is intended. It is possible to use RF network analyzers for measuring a variety of components ranging from filters and frequency sensitive networks, to devices such as transistors, mixers and any RF orientated device.
Typically RF network analyzers are more usually associated with microwave type frequencies. However the RF network analysers that are available cover down to much lower frequencies than this, and some are even able to make measurements at frequencies down to 1 Hz.
Types of RF network analyzer
Within the broad scope of RF network analyzers, there are various types of instrument which can be bought and used. These types of RF network analyzer are very different, but they are all able to measure the parameters of RF components and devices but in different ways:
- Scalar network analyzer (SNA): The scalar network analyzer, SNA is a form of RF network analyzer that only measures the amplitude properties of the device under test - i.e. its scalar properties. In view of this it is the simpler of the various types of analyser. Read more . . .
- Vector network analyzer (VNA): The vector network analyzer, VNA is a more useful form of RF network analyzer than the SNA as it is able to measure more parameters about the device under test. Not only does it measure the amplitude response, but it also looks at the phase as well. As a result vector network analyzer, VNA may also be called a gain-phase meter or an Automatic Network Analyzer. Read more . . .
- Large Signal Network Analyzer (LSNA): The large signal network analyzer, LSNA is a highly specialised for of RF network analyser that is able to investigate the characteristics of devices under large signal conditions. It is able to look at the harmonics and non-linearities of a network under these conditions, providing a full analysis of its operation. A previous version of the Large Signal Network Analyser, LSNA was known as the Microwave Transition Analyzer, MTA.
The various types of RF network analyzer are quite different in their make-up and the way in which they are able to make measurements. The scalar network analyzer is the least expensive, although not cheap, but it also provides the least information. The vector network analyzer is able to provide considerably more information, but these RF network analyzers are also considerably more expensive.
Difference between RF network analyzers and spectrum analyzers
Although there are many similarities between network analyzers and spectrum analyzers, there are also several major differences, especially in the types of measurements that are made. In particular they make very different types of measurement. In the first instance a spectrum analyzer is intended for analysing the nature of signals that are fed into them. A network analyzer, on the other hand generates a signal and uses this to analyze a network or device.
RF Network analyzers are used to measure components, devices, circuits, and sub-assemblies. An RF network analyzer will contain both a source and multiple receivers. It will display amplitude and often phase information (frequency or power sweeps) and normally in a ratio format. An RF network analyzer looks for a known signal, i.e. a known frequency, at the output of the device under test, since it is a stimulus response system. With vector-error correction, network analyzers provide much higher measurement accuracy than spectrum analyzers.
By contrast to RF network analyzers, spectrum analyzers are normally used to measure the characteristics of a signal rather than a device. The parameters measured may include: signal or carrier level, sidebands, harmonics, phase noise, etc. They are most commonly configured as a single channel receiver, without a source. Because of the flexibility needed to analyze signals, spectrum analyzers generally have a much wider range of IF bandwidths available than most RF network analyzers.
Spectrum analyzers can be used for testing networks such as filters. To achieve this they need tracking generator. When used in this way, spectrum analyzers can be used for scalar component testing (magnitude versus frequency, but no phase measurements). With spectrum analyzers, it is easy to get a trace on the display, but interpreting the results can be much more difficult than with a network analyzer.
RF network analyzers are a particularly useful item of RF design test equipment. They enable the RF designer to see many aspects about the performance of a component or network and in this way the circuit can be designed to ensure the optimum performance. Typically RF network analyzers are not used within production environments because of the complicated nature of the measurements that are made and also the cost of the equipment.
By Ian Poole
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