Air Gap Corrections in Clamped Stripline in Plane Permittivity Extraction
Air gap corrections eliminate systematic two to six percent dielectric underestimation in clamped stripline tests, preventing finished board impedance failures.
Two-Thickness Method
Permittivity Characterization
The extraction of the complex dielectric constant of a printed circuit substrate by comparing measurements of two transmission lines of identical width but different dielectric thicknesses represents a highly reliable methodology in board materials testing. Using the two-thickness method eliminates the measurement errors caused by conductor loss and surface roughness by calculating the ratio of the two propagation characteristics. This technique allows for the precise determination of dielectric properties at high microwave frequencies.
Materials engineers use these extracted parameters to refine simulation models and ensure that simulated signal integrity matches the physical reality of the manufactured board.
Analytical Extraction
By comparing the phase and attenuation of the two signals, the mathematical model separates the contribution of the laminate dielectric from that of the copper conductor. This is particularly valuable because copper surface roughness behaves like a frequency-dependent dielectric loss in conventional single-thickness tests. Using this dual-sample approach provides a clean separation of loss mechanisms.
Quality Control
This measurement strategy is widely used by high-performance laminate manufacturers to verify the consistency of their dielectric materials across different production runs. The results are used to populate simulation tools with highly accurate substrate data, ensuring that designed trace impedances match fabricated boards. By using this method, engineers can avoid the costly design iterations caused by relying on nominal or estimated dielectric values.