Insertion loss – represented by the S21 parameter indicated in the figure below – quantifies the power loss introduced by the device when a signal passes through it; it is an assessment on the impact of the device based on the transmitted signal's amplitude.
Lower insertion loss values indicate better device performance, as the device minimally affects the signal amplitude.
Note that your best measurements always start with a calibration. For more information, see the application note "Why Calibration Matters" found on the Bird Vector Network Analyzer landing page.
To measure the insertion loss connect port 1 of the VNA to the input of your device then connect port 2 to the output of your device, similar to how the filter in the image below is connected.
From the VNA software main menu, you would then change your Measurement selection to 'S21' scattering parameters but leave the Format as 'Log Mag' since loss is typically measured in decibels (dB).
You can then add markers to the active trace at your frequencies of interest. For a filter, it may be your center and corner frequencies (as below).
Bear in mind that some devices may need some additional attention. For instance, measuring insertion loss on a directional coupler would require you to ensure the unused ports are terminated with a load. If you have a VNA with just two ports, you will add the terminations (as below). If you have a four-port VNA, you have the option of connecting the two additional ports since they offer 50-ohm output impedance.
Comments
Please sign in to leave a comment.