The following are some advantages of using S-parameters: The basic measurements to determine the S-parameters are familiar and well established microwave measurements: reflection coefficient, attenuation gain , phase S-parameters are analytically convenient; they allow for calculations of system performance by cascading the individual components. Flow-graph analysis can be used, which simplifies the analysis of a microwave system.
Was this helpful? Thus S 21 means the response at port 2 due to a signal at port 1. The most common "N-port" networks in microwaves are one-port and two-port networks.
Three-port network S-parameters are easy to model with software such as Agilent ADS, but three-port S-parameter measurements are extremely difficult to perform with accuracy. Measured multi-port S-parameters are typically available from vendors for amplifiers and other devices but, as always, make sure you check your answers for reasonableness.
Let's examine a two-port network. The signal at a port, say port 1, can be thought of as the superposition to two waves traveling in opposite directions. By convention each port is shown as two nodes so as to give a name and value to these opposite direction waves.
The variable a i represents a wave incident to port i and the variable b j represent a wave reflected from port j. Don't get all hung up on how two signals can occur at the same node! The magnitude of the a i and b j variables can be thought of as voltage-like variables, normalized using a specified reference impedance. This is very convenient since the square of these magnitudes are then equal to the power level of the waves. Remember, S-parameters don't mean much unless you know the value of the reference impedance it's frequently called Z 0.
If we assume that each port is terminated in the reference impedance Z 0 , we can define the four S-parameters of the 2-port as:. Here's the matrix algebraic representation of 2-port S-parameters:. If we want to measure S 11 , we inject a signal at port one and measure its reflected signal. If we want to measure S 21 , we inject a signal at port 1, and measure the resulting signal power exiting port 2. For S 12 we inject a signal into port 2, and measure the signal power leaving port 1, and for S 22 we inject a signal at port 2 and measure its reflected signal.
Did we mention that all the a and b measurements are complex numbers? It isn't always necessary to keep track of the angle of the S-parameters, but complex S-parameters are a much more powerful tool than magnitude-only S-parameters, and the math is simple enough either way. By the way, these complex numbers are sometimes called vectors, hence the term vector network analyzers VNA. S-parameter magnitudes are presented in one of two ways, linear magnitude or logarithmic based decibels dB.
Because S-parameters are complex voltage ratios, the formula for decibels in this case is. The angle or phase of a complex S-parameter is almost always presented in degrees but, of course, radians are possible. When we are talking about networks that can be described with S-parameters, we are usually talking about single-frequency networks. S22 is the output port voltage reflection coefficient.
The S-parameter matrix can be used to determine reflection coefficients and transmission gains from both sides of a two port network.
This concept can further be used to determine s-parameters of a multi port network. S-parameters or scattering parameters are used to describe how energy can propagate through an electric network. S-Parameters are used to describe the relationship between different ports, when it becomes especially important to describe a network in terms of amplitude and phase versus frequencies, rather than voltages and currents.
S-Parameters are used to show a complicated network as a simple black box, and to easily present what happens to the signal in that network. The S-parameters can be saved e.
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Go Ask a Question. Submit Cancel. What are S-Parameters? RF Basics. Can you answer this question? Mohit Garade - Altair Nov 24, For a two port network, s-parameters can be defined as S11 is the input port voltage reflection coefficient S12 is the reverse voltage gain S21 is the forward voltage gain S22 is the output port voltage reflection coefficient The S-parameter matrix can be used to determine reflection coefficients and transmission gains from both sides of a two port network.
Sony Semiconductor Israel Israel. A: S-parameters and the resultant scattering matrix is an arrangement which quantifies how RF energy propagates through a multi-port network. For example, S21 is a measure of the signal coming out port 2 relative to the RF stimulus entering port 1. When the numbers are the same e. A: The amplitude and phase information quantifies the reflection and transmission characteristics of the DUT. Some of the commonly measured factors are magnitude only scalar , while others are vectors both magnitude and phase.
For example, return loss is a scalar measurement of reflection, while impedance results from a vector reflection measurement. Others, such as group delay, are solely phase-related measurements. Note that the S-parameters are a function of frequency of the device or circuit being assessed; a single set of four numbers real or complex does not characterize the situation.
Instead, the test result is a graph or table for each of the four parameters as a function of frequency Figure 3. A: Absolutely not.
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