R&S ZNL, Руководство пользователя

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VNA concepts and features
R&S
®
ZNL/ZNLE
228 User Manual 1178.5966.02 ─ 19
Mixed-mode parameters for different test setups
Which types of mixed mode parameter are available depends on the measured device
and the port configuration of the analyzer. The following examples of mixed mode
parameters can be measured with a 2-port analyzer.
1. DUT with only single-ended ports: No balanced port definition necessary, the ana-
lyzer provides single-ended multiport parameters.
2. DUT with one balanced port: Only reflection and mode conversion measurements
with differential and common mode parameters.
9.3.7 Stability factors
The stability factors K, μ1 and μ2 are real functions of the (complex) S-parameters,
defined as follows:
| | 2
| | | | | | 1
:
21 12
2
21 12 22 11
2
22
2
11
S S
S S S S S S
K
 
     

| | | ) ( |
| | 1
:
21 12 21 12 22 11 11 22
2
11
1
S S S S S S S S
S
      



| | | ) ( |
| | 1
:
21 12 21 12 22 11 22 11
2
22
2
S S S S S S S S
S
      



where denotes the complex conjugate of S.
Stability factors are calculated as functions of the frequency or another stimulus
parameter. They provide criteria for linear stability of two-ports such as amplifiers. A lin-
ear circuit is said to be unconditionally stable if no combination of passive source or
load can cause the circuit to oscillate.
●
The K-factor provides a necessary condition for unconditional stability: A circuit is
unconditionally stable if K>1 and an additional condition is met. The additional con-
dition can be tested with the stability factors μ
1
and μ
2
.
●
The μ
1
and μ
2
factors both provide a necessary and sufficient condition for uncondi-
tional stability: The conditions μ
1
>1 or μ
2
>1 are both equivalent to unconditional
stability. This means that μ
1
and μ
2
provide direct insight into the degree of stability
or potential instability of linear circuits.
Measurement results