Signal Reduction
Signal power reduction along a transmission line represents a primary factor in the design of high-speed circuit boards. This reduction in signal amplitude, known as insertion loss attenuation, is caused by the combined effects of dielectric absorption and conductor losses. The loss increases as the frequency of the signal rises, which limits the effective length of high-speed traces.
Designers calculate this loss to ensure that the received signal meets the noise margin requirements of the receiving component.
Substrate Dispersion
Dielectric material properties and conductor surface roughness govern the rate of signal decay as electromagnetic waves propagate. At gigahertz frequencies, insertion loss attenuation becomes more severe because of the molecular polarization within the fiberglass substrate. Rough copper interfaces also lengthen the signal path, which increases resistive loss through the skin effect.
Advanced low-loss laminates and smooth copper foils are used to minimize these dielectric and conductor losses in high-frequency designs.
Measurement Method
Vector network analyzers measure the change in signal amplitude across a test coupon to determine compliance with performance specifications. Engineers connect high-frequency probes to the test vehicle to sweep a range of frequencies and measure the scattering parameters. The results are compared against the maximum allowable limits defined in the design specification.
If the measured signal reduction exceeds the limit, the board laminate is changed or the trace dimensions are recalculated to achieve acceptable performance. This testing ensures that the manufactured board supports the high-speed communication protocols required by the system. Technicians use microsection analysis alongside the electrical test to verify that the trace geometry and dielectric thickness match the simulation models.
Such verification prevents the fabrication of boards that experience excessive signal loss at the operation frequencies.
