This section provides overview, applications, and principles of network analyzers. Also, please take a look at the list of 14 network analyzer manufacturers and their company rankings.
A network analyzer is a device that evaluates the network characteristics of a device under test (DUT).
Specifically, it can measure the attenuation and impedance of the input signal to the DUT. In particular, it can evaluate the high-frequency characteristics of electronic components, etc., and has a wide range of applications, including transmission devices.
The output of the network analyzer is represented by the S-parameter (scattering parameter), which defines the physical quantities forward reflection (S11), forward transmission (S21), reverse transmission (S12), and reverse reflection (S22).
Network analyzers are broadly classified into scalar network analyzers and vector network analyzers (VNA), of which vector network analyzers (VNA), which provide not only amplitude information but also phase information, have a wider range of uses.
The advantages of network analyzers for high-frequency applications are used in the development of matching circuits for high-frequency amplifiers. Here, the design is based on accurate S-parameters for each amplifier, antenna, and filter.
In many cases, the network analyzer is also used to evaluate impedance matching. This is because impedance mismatch in transmission lines of each device or cable in a high frequency handling circuit network can cause power loss or signal distortion.
A network analyzer is equipped with a signal source, a signal separator, a directional coupler, and at least three receivers.
The output of the DUT is measured at a third receiver (transmission signal B). Evaluation is performed by comparing the signals (e.g., S11 is defined by A/R and S21 by B/R).
Accurate measurement of the network analyzer is ensured by precise calibration. For calibration, a standard device with known characteristics is used. A commonly used calibration method is the SOLT method, in which a short-circuit, open-circuit, and the load-capable standard is coupled to a reference plane in a direct connection (thru).
Since this is a very precise measurement, care must be taken to avoid measurement errors in various aspects such as connector tightening torque, ambient temperature, input signal, cable stability, etc.
There are two types of network analyzers: vector network analyzers (VNA) and scalar network analyzers. Vector network analyzers are widely used these days.
Network analyzers have a method of measuring amplitude changes in transmission and reflection measurements called S-parameters. S-parameters are also called S-matrices, and there is a numbering system for their definition. The numbering scheme is "Sij i=output port, j=input port," where S11 represents the measurement of a signal incident at port 1 that has been transmitted to port 1, S12 represents the measurement of a signal incident at port 2 that is transmitted to port 1.
The S parameter can be measured by using a VNA measuring instrument. However, the VNA must be calibrated using several calibration methods before measurement.
The basic method of VNA calibration is to use three standard instruments. Widely known calibration methods include the SOLT calibration method, the UnKnown Thru calibration method, and the TRL calibration method described above.
Impedance is an important parameter used to characterize electronic circuits, electronic components, and electronic materials and is the amount of alternating the current that interrupts a circuit or other device at a certain frequency. There are various types of impedance measurement methods, each with its own advantages and disadvantages.
The measurement method must be selected in consideration of the frequency range required for the measurement and the measurement conditions of the impedance measurement range. Measurement methods include the bridge method, resonance method, I-V method, network analysis method, time domain network analysis method, and automatic balanced bridge method.
The bridge method is explained as an example. The advantages of the bridge method are its high accuracy (around 0.1%), its ability to cover a wide frequency range with multiple measuring instruments, and its low cost. On the other hand, the demerit of the bridge method is that it requires a balance operation, and a single unit can cover only a narrow range of frequencies. The bridge method's measurement frequency range is approximately 300 MHz DC.
The maximum frequency extension of network analyzers now extends into the sub-THz band (220 GHz). This is because it is predicted that the next generation communication standard, 6G, will most likely use the 140 GHz band, known as the D-band.
However, because of its high frequency, the sub-THz band is susceptible to electrical length errors and parasitic elements, making total calibration accuracy, including RF probes and cables, extremely important.
In reality, the frequency range that can be calibrated at one time is often limited, and manufacturers are competing to develop easy-to-use measuring instruments, including the handling of data between calibrations and the addition of frequency extenders dedicated to the millimeter wave band.
Network analyzers are generally used to evaluate the impedance of DUTs and S-parameters, which are small signals. Therefore, models that enable network analyzers to perform modulation analysis, which is mainly handled by conventional spectrum analyzers, are gradually being released.
In the future, network analyzers will be used not only for impedance and S-parameter evaluation but also for evaluating switches, filters, high-frequency (RF) amplifiers, low-noise amplifiers (LNA), and other RF front ends, including large-signal analysis and modulation analysis.
*Including some distributors, etc.
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