Loss Measurement
High frequency evaluation procedures calculate the specific insertion loss of printed circuit board materials using multiple lengths of identical traces. The delta-l method extracts the signal attenuation per inch by subtracting the total loss of a short trace from the loss of a much longer counterpart. This operation eliminates the influence of connectors and measurement probes from the final data set.
It is applied during material validation before mass manufacturing begins.
Accuracy Limits
Variation in board manufacturing affects the repeatability of these measurements across different lots. Because the delta-l method assumes that the two trace lengths are identical in cross-section and roughness, any fabrication error between them creates an artificial shift in the calculated loss value. Standard practice involves using neighboring traces on the same layer to minimize environmental differences.
Test coupons provide data. Calibration ensures validity.
Computational Steps
Software tools analyze the raw phase and magnitude data to distinguish the dielectric loss from the conductive skin effect. By applying the delta-l method, engineers can predict the reach of high-speed digital links without building full application prototypes. Accurate modeling relies on high-resolution data collection at the upper edges of the signal bandwidth.
Clean signals improve results.
