3.2 Transformation to System Impedance

In some scenarios, using a system impedance instead of matching directly to the target value is preferred. An example is the connection of a SAW filter to an LNA. The SAW filter has a certain complex impedance, which are available in the technical documents. The SAW manufacturer typically recommends a matching network to 50Ω impedance. Typically, this does not fit the input of the LNA, and it must be matched to the 50Ω impedance. This point is called the system impedance. From the technical point of view, this transformation is not needed, as it is possible to directly transform from the complex impedance of the LNA to the value of the SAW. This can be a difficult task with complex equations. Therefore, using the system impedance is helpful. The big advantage is the defined point that can be used to perform the matching for both RF components, as shown in the following figure.