Quasi Optical Free Space Calibration and Permittivity Extraction Methods
Quasi-optical free-space calibration extracts complex permittivity by focused Gaussian beam measurements to qualify mmWave materials for regulatory filing.
Quasi Optical Calibration
Meaning
Electromagnetic measurement protocols establish reference planes for high-frequency signals propagating through free space rather than through closed waveguides or coaxial lines. Using quasi optical calibration techniques allows engineers to characterize antennas, filters, and materials at submillimeter and terahertz frequencies. This process employs mirrors and focusing lenses to shape the signal into a beam that behaves similarly to light.
Standard calibration models like line-reflect-line are adapted to these beam-forming networks to isolate instrument drift from the device under test.
System Configuration
Precision positioning stages align the calibration standards with the focal points of the focusing lenses. This alignment ensures that the wave-fronts are planar at the reference plane. Laser trackers verify the spatial coordinates of the components to prevent phase errors during the test run.
Mathematical Error
Vector network analyzers apply correction matrices to the measured scattering parameters to de-embed the effects of the horn antennas and the surrounding air paths. Systematic errors like source match and transmission tracking are mathematically removed. This step improves the accuracy of both transmission and reflection measurements.
Target Selection
Metal plates act as perfect reflection standards, while empty line measurements provide the transmission reference. High-precision dielectric blocks are utilized to verify the phase response.