S-Parameters; Additional Examples - Anritsu MS2024B Manual

3-2 S-Parameters

3-2 S-Parameters
To simplify the description of the types of measurements a VNA can make, the reflection and
transmission measurements are defined in terms of scattering parameters, or S-parameters.
For a 2-port network, four fundamental S-parameters can be measured, and they are defined
as S . For a 2-port VNA, measurements of signals leaving Port 1 are called forward
XY
measurements, and those leaving Port 2 are called reverse measurements. Signals that leave
and return to the same port are designated reflection measurements, and those that leave one
port and return to another port are designated transmission measurements. S-parameters
are an abbreviated designation for these measurements, and are used as shown in the
following list:
• S : Forward Reflection
11
• S : Forward Transmission
21
• S : Reverse Transmission
12
• S : Reverse Reflection
22
The first number (X) in S
second number (Y) is the port number from which the signal is leaving. The S-parameter is a
ratio of these two signals.

Additional Examples:

: Forward Reflection represents the measurement in which the signal leaves port 1 and
S
11
is reflected back to port 1.
: Forward Transmission represents the measurement in which the signal leaves port 1
S
21
and is transmitted to port 2.
: Reverse Transmission represents the measurement in which the signal leaves port 2
S
12
and is transmitted to port 1.
: Reverse Reflection represents the measurement in which the signal leaves port 2 and
S
22
is reflected back to port 2.
3-2
is the port number into which the signal is being injected, and the
XY
PN: 10580-00289 Rev. K
VNA Fundamentals
Vector Network Analyzer MG