S parameters S11,S22,S12,S22 | S Parameter measurements

This page covers basic measurement of S parameters viz. S11, S12, S22, S21. It covers setup used in S-parameter measurements which covers S11, S12, S22, S21.

As we know a vector signal consists of both amplitude and phase information. When a signal is passed from linear of non-linear device which we call it DUT (Device Under Test) in our discussion; the characteristics of signal will alter. The amplitude/phase of output signal is different compare to input signal. S-parameter convey both of these information i.e. amplitude and phase.

S Parameters-S11,S12,S22,S21

Amplitude variation information provides insertion loss while timing variation provides phase shift. S parameters are complex matrix which helps us analyzing reflection and transmission characteristics in the frequency domain.

There are four types of S parameters of a two port device. The convention is letter "S" followed by two numeric digits first one is the port from where output is derived while second one is the port where input is to be fed.
For EXAMPLE: S21 -> Here Port-2 is the output port and Port-1 is the input port.

Following are the types of S parameter measurements carried out.
• Transmission measurement parameters viz. S11,S22
• Reflection measurement parameters viz. S21, S12

S11 and S22 provides us following useful information.
• Return loss or reflection coefficient,
• Impedance and Admittance,
• VSWR of input and output ports

S21 and S12 provides us following useful information.
• Gain/Loss (i.e. insertion loss),
• Phase and Group Delay(i.e. delay time)

Setup block diagram for S Parameters measurement

The VNA known as Vector Network Analyzer is used for measurement of S parameters. The figure-2 depicts internal block diagram of VNA.

S Parameters Measurement setup

Following are the four S parameters measured using this VNA.
➨S11 Input Reflection Coefficient: Measured by taking ratio of A & R1 .
➨S22 Output Reflection Coefficient: Measured by taking ratio of B& R2 .
➨S21 Transmission Insertion loss: Measured by taking ratio of B & R1 . (Output at port-2 and input at port-1)
➨S12 Tranmission Isolation: Measured by taking ratio of A & R2 . (Output at port-1 and input at port-2)

S parameters are obtained by measuring amplitude and phase information using four receivers viz. R1, R2, A, and B inside the Vector Network Analyzer (VNA).

Links to useful Measurements

Following are the links to other useful measurements available on Test and Measurement World website.
Difference between EVM vs subcarriers and EVM vs symbols
Current measurement vs Voltage measurement
Inductance measurement vs Capacitance measurement
Difference between Power and Energy measurements
EMC measurement vs EMI measurement
Electric and Magnetic Field Measurements

What is difference between or comparison between

Following links mention difference or comparison between various equipments:
comparison between VSG and VSA
DIfference between SNA ans VNA
Oscilloscope Bandwidth versus Rise time
Oscilloscope vs Logic Analyzer
Difference between Oscillscope types
Comparison between spectrum and network analyzer