In-Situ Free-Space Dielectric Testing of Unclad Substrates
Non-destructive free-space characterization evaluates bulk dielectric properties of raw unclad laminates without etched coupon waste or copper interface errors.
Thru Reflect Line
Calibration Algorithm
Calibration routines using three distinct standards determine the systematic errors of a vector network analyzer during high-frequency microstrip measurements. This thru reflect line method is especially suited for on-board and fixture-based measurements where standard coaxial calibration kits cannot be used. By using the transmission lines of the board itself as standards, the technique places the measurement reference planes directly at the device terminals.
This approach eliminates the parasitic effects of the test fixtures.
Measurement Accuracy
Mathematical matrix calculations use the measurements of the three standards to isolate the true scattering parameters of the device. During the thru reflect line procedure, the analyzer measures a direct connection, a highly reflective open or short, and a short transmission line of known length. This calculation is essential for characterizing high-frequency microstrip structures.
Physical Implementation
Board layout constraints dictate the design of the calibration standards to match the substrate properties. The lines must be fabricated on the same laminate and routing layer as the device under test to ensure identical characteristic impedance. Any variation in dielectric constant or copper thickness between the standards and the test traces invalidates the thru reflect line calibration.
Engineers must also design the line length to be a quarter-wavelength at the center of the measurement band. This geometric precision ensures that the phase shift remains within the acceptable window for error correction, which preserves signal integrity measurements.