In electrical engineering, impedance is the ratio of voltage to current with the consideration of phase angle. According to Ohm’s law V= IR, where V – voltage, I is the current and R is the resistance of the network. In RF, the idea of impedance matching is to equalizing the source and load impedance for maximum power transfer. Impedance is represented as Z and is complex than just the resistance of the network. In simple explanation, impedance matching is to making source and load impedance as similar as possible in order to minimize losses.
S-parameters are mathematical representation of energy propagation within a multiport electrical network. It is written as a complex matrix file also knows as scattering parameters. S-parameter file represents full combination of the reflection and transmission parameters in a multiport network with frequency component. It gives an idea of how the DUT behaves with a signal in both forward and reverse direction.