Radio Frequency Interconnect Loss Driven by Substrate Dielectric Degradation Mechanisms
Substrate moisture absorption increases dielectric loss tangent, raising RF interconnect insertion loss and reducing long-term wireless link margins.
Resonant Ring Method
Meaning
Dielectric characterization of substrate materials utilizes a closed-loop microstrip structure to identify permittivity and loss at specific frequencies. Resonant ring method testing involves measuring the transmission through a circular conductor that is loosely coupled to input and output feed lines. Resonances occur when the mean circumference of the ring is an integer multiple of the guided wavelength.
This technique is particularly effective for evaluating thin laminates used in high-frequency applications.
Excitation Mode
Signal energy enters the ring through a small gap that prevents the feed lines from loading the resonator. The resonant ring method relies on the constructive interference of waves traveling around the circle. Sharp peaks in the transmission spectrum indicate the resonant frequencies of the structure.
Extraction Logic
Frequency measurements of the peaks allow for the calculation of the effective permittivity of the substrate. The width of these peaks at the 3-decibel point provides the quality factor, which relates to the total dielectric and conductor loss. This data is used to model the material behavior in simulation software.
Measurement Precision
Eliminating end-effect errors associated with linear resonators makes this approach more accurate for broadband characterization. The resonant ring method provides a repeatable way to compare different batches of material from a single supplier. Manufacturers use these results to ensure that the dielectric constant remains within the tolerance specified for the product.