Gain (dB or ratio) and phase (degrees or radians) S parameters are analogous to frequency response functions, but the terms are used at high and lower frequencies, respectively. S-parameters can be converted to impedance by taking the ratio of (1 + S 11) to (1- S 11) and multiplying the result by the characteristic impedance (often 50 or 75 ohms).Ī Smith chart is used to convert between impedance and S-parameters. S 12 is the reverse transmission gain (from output to input). S 22 is the reflection coefficient of the output S 11 is the reflection coefficient of the input Port, hence the S-parameter for the input reflection is designated S 11.įor a two port network, (assume use of matched loads) Likewise, for reflected waves, the signal comes in and out of the same If you’re dropping the resistance, Xp RL / Q 4. Compute the required circuit Q by (1 + Q2) m, or 3 L I F1. To the incident wave on port 1 is designated S 21. Smith Chart basics Scattering Parameters EE142-Fall 2010 4 Matching Network Design 1. S-parameters can be considered as the gain of the network, and the The value of the wave multiplied by the relevant S-parameter. Travels through a network, the output value of the network is simply Electronic Packaging and Interconnects Series, vol 2. Parameter (which is analogous to the gain of the network), thus giving In: Package Electrical Modeling, Thermal Modeling, and Processing for GaAs Wireless Applications. is gain and phase are changed) by the scattering When the incident wave travels through the network, its value is The reflected wave isĭesigned by b n, where n is the port number. (applied) and reflected wave are measured.
Where n is the port number of the network. The incident waves are designated by the letter a n, For this reason, S-parameters are often called complex scattering parameters.
Important to note that frequency is implied, and that the complex gain (i.e. S-parameters are normally measured as a function ofįrequency, so when looking at the formulae for S-parameters it is S- parameters are normally used to characterize highįrequency networks, where simple models valid at lower frequenciesĬannot be applied. A set of parameters describing the scatteringĪnd reflection of traveling waves when a network is inserted into a
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