Special types of network analyzers can also cover lower frequency ranges down to 1 Hz. A VNA is a form of RF network analyzer widely used for RF desig
Special types of network analyzers can also cover lower frequency ranges down to 1 Hz. A VNA is a form of RF network analyzer widely used for RF design applications. VNAs are the most common type of network analyzers, and so references to an unqualified “network analyzer” most often mean a VNA. The MTA was commercialized before electrical circuit analysis problems pdf LSNA, but was lacking some of the user-friendly calibration features now available with the LSNA.
The basic architecture of a network analyzer involves a signal generator, a test set, one or more receivers and display. In some setups, these units are distinct instruments. Nearly all modern network analyzers have a built-in signal generator. High-performance network analyzers have two built-in sources.
The test set takes the signal generator output and routes it to the device under test, and it routes the signal to be measured to the receivers. It often splits off a reference channel for the incident wave. The result is better control of the signal generator’s output and better measurement accuracy. Directional couplers or two resistor power dividers are used for signal separation. The receivers make the measurements. A network analyzer will have one or more receivers connected to its test ports. Some analyzers will dedicate a separate receiver to each test port, but others share one or two receivers among the ports.
For the SNA, the receiver only measures the magnitude of the signal. A receiver can be a detector diode that operates at the test frequency. The simplest SNA will have a single test port, but more accurate measurements are made when a reference port is also used. The reference port will compensate for amplitude variations in the test signal at the measurement plane. It is possible to share a single detector and use it for both the reference port and the test port by making two measurement passes. For the VNA, the receiver measures both the magnitude and the phase of the signal.
VNA needs at least two receivers. The usual method down converts the reference and test channels to make the measurements at a lower frequency. A VNA requires at least two receivers, but some will have three or four receivers to permit simultaneous measurement of different parameters. With the levels of processing that are available today, some very sophisticated solutions are available in RF network analyzers. Here the reflection and transmission data is formatted to enable the information to be interpreted as easily as possible. Most RF network analyzers incorporate features including linear and logarithmic sweeps, linear and log formats, polar plots, Smith charts, etc.
The test port connectors provided on the VNA itself are precision types which will normally have to be extended and connected to P1 and P2 using precision cables 1 and 2, PC1 and PC2 respectively and suitable connector adaptors A1 and A2 respectively. The position of switch SW1 sets the direction that the test signal passes through the DUT. Similarly, signals leaving P2 pass via A2, PC2 and DC2 to RX TEST2. All of the complex receiver output signals are fed to a processor which does the mathematical processing and displays the chosen parameters and format on the phase and amplitude display. 2 test channels, one as a reference and the other for measurement. When SW1 is set to position 2, the test signals are applied to P2, the reference is measured by RX REF2, reflections from P2 are coupled off by DC2 and measured by RX TEST2 and signals leaving P1 are coupled off by DC1 and measured by RX TEST1.