Vector network analyzer (VNA) overview
Vector network analyzer (VNA) measurement systems are used to fully characterize the linear behavior of two port devices or networks. Device characteristics include the magnitude and phase data of the transmission or reflection parameters that are required to determine complex impedance, both resistive and reactive components, shown in Figure 1. A network’s behavior is linear when (1) a linear change in the input results in a linear change in the output, and (2) the output, resulting from multiple input signals, is the same as the sum of the outputs resulting from independent input signals. Some examples of linear networks are filters, amplifiers, cables and isolators.
A network analyzer measurement system can be divided into four major parts shown in Figure 2:
1.A signal source providing the incident signal
2.Signal separation devices to separate the incident, reflected and trans- mitted signals, and then down converts the microwave signals to a lower intermediate (IF) signal
3.A receiver to attain the IF signal and down convert it to DC
4.A signal processor and display section that processes the data and displays information on a CRT
Incident
DUT
| Transmitted |
Reflected |
|
Reflection | Transmission |
(Reflected/incident): | (Transmitted/incident): |
Input SWR | Gain/loss |
Return loss | Isolation |
Input/output impedance | Insertion phase |
Reflection coefficient | Group delay |
Figure 1. Device characterization
Incident
| DUT |
Source | Reflected |
|
Transmitted
Signal separation
Incident
Reflected Transmitted
Receiver/Detector
Processor/Display
Figure 2. Network analyzer configuration
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