Scattering Coefficient
Scattering coefficients quantify the reflection and transmission of electromagnetic waves at defined network ports. Engineers use high frequency s-parameters to characterize the performance of circuit components, connectors, and PCB traces across the microwave and millimeter-wave spectrum. These values are expressed as complex numbers, capturing both the magnitude and the phase of the signal as it travels through the system.
Port Definition
Measurement of a device requires the identification of specific input and output locations. For high frequency s-parameters, the data is typically presented in a matrix where the index describes the interaction between ports. S11 represents the signal reflected back from the first port, while S21 describes the signal that passes through to the second port.
These measurements allow designers to identify impedance mismatches that cause signal loss or unwanted reflections. Modern simulation tools import these data sets to predict the behavior of complex interconnects before the hardware is built. Accurate data acquisition requires the use of high quality cables and calibrated test equipment.
Data Acquisition
Precision in the high frequency range depends on the removal of systematic errors from the measurement setup. Because high frequency s-parameters are sensitive to small physical changes, the test environment must be carefully controlled for temperature and mechanical stability. Probing techniques or surface mount connectors are used to interface with the device under test.
The resulting plots show insertion loss and return loss across the entire frequency band of interest.
