S-parameter extraction of passive sub-circuits using computed tomography scans and measured substrate material parameters

This paper presents a method for S-parameter extraction of passive sub-circuits embedded in complex microwave circuits. We employed computed tomography (CT) scans and measured substrate material parameters. The principle is based on the automatic reconstruction of CAD models from CT image data. Such CAD models represent the geometry of the actual manufactured passive microwave circuits and are suited for 3D electromagnetic field simulation to extract the S-parameters of these devices non-destructively. It is shown that by supplementing the simulation model with measured material parameters the agreement between the simulated S-parameters and the measured S-parameters can be improved. The proposed method has been applied to a passive 90° hybrid coupler, which is embedded in a hybrid power amplifier circuit.