Mid Loss Laminates That Outrun Their Price Class
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Split-Post Cavity Resonator
Material Testing
Dielectric characterization of thin laminate sheets requires highly accurate measurement methods that do not damage the test sample. The split-post cavity resonator is a laboratory test fixture used to measure the dielectric constant and dissipation factor of thin PCB substrates at microwave frequencies. This device consists of two halves of a resonant cavity that are separated by a small gap where the test laminate is placed.
Microwave designers and board material manufacturers rely on this tool to verify the electrical properties of laminates before they are used in high speed board fabrication.
Fixture Mechanism
Resonant frequency shifts and quality factor changes are measured when a sample is inserted into the gap. When a split-post cavity resonator is operated, a microwave signal is swept through the cavity to find its resonant frequency and quality factor. When the sample is inserted, the dielectric material interacts with the electromagnetic field, shifting the resonant frequency downward and reducing the quality factor.
By analyzing these changes, the software calculates the precise dielectric constant and loss tangent of the material, providing a highly repeatable test method.
Calibration Method
Calibration of the test fixture is necessary to ensure measurement accuracy over time. The system is first calibrated empty to establish a baseline resonant frequency and quality factor. This step removes the effect of air humidity and temperature variations from the final measurement calculation.