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.
Gaussian Beam Waist
Focal Plane
Converging wave fronts in a focused microwave system reach a point of maximum intensity and minimal diameter. The gaussian beam waist represents the radius at this narrowest point where the wavefront is perfectly planar. At this location, the power density is at its peak and the phase distribution is uniform across the aperture.
Measurement Zone
Material characterization in free-space systems requires placing the sample exactly at the location of highest field concentration. Using the gaussian beam waist as the reference point ensures that the incident energy interacts with a flat phase front rather than a curved one. This positioning minimizes diffraction effects at the edges of the substrate under test.
If the sample is too large or too small relative to the spot size, the transmission and reflection data lose accuracy. A smaller waist allows for the testing of smaller coupons but increases the divergence angle of the beam. Operators verify the position of the waist by observing the stability of the scattering parameters during a longitudinal shift of the sample fixture.
Beam Divergence
Far from the focal point, the energy spreads out at an angle determined by the wavelength and the initial width. The gaussian beam waist defines the confocal parameter, which is the distance over which the beam remains relatively collimated. Practical antenna designs for microwave microscopy rely on lenses or reflectors to create this convergence.