# Timing Analyses in FWE Evaluation
## 2 Problem Statement and Issues
### The Fiberglass Fabrics Effect
However, this method has limitations, such as not providing direct information about the frequency content of the signal. Frequency domain analysis is a method that investigates the frequency content of signals, revealing the frequency components that make up a signal and their intensity. The advantages of frequency domain analysis lie in studying the frequency spectrum, identifying dominant frequencies, and evaluating how a system responds to different frequencies. However, it is limited by its inability to provide information about the timing or sequence of events over time. Therefore, it is crucial to study both cases. Time domain analysis and frequency domain analysis offer different perspectives on system behavior. Combining both methods provides a more comprehensive understanding. Some faults or issues may be more evident in a time domain analysis, while others may be better understood by exploring their frequency content. In the design and analysis of systems, understanding behavior in both domains can contribute to optimizing performance and stabilizing the system. By approaching both methods, more robust and complete conclusions can be drawn about the characteristics of the analyzed signals and systems. Article [1] presented only frequency domain analysis. We have centralized the results obtained in [1] in two tables: Table 3 for reflections loss and Table 4 for insertion loss. Figure 15: (a) Eye diagram homogeneous substrate vs. inhomogeneous substrate—microstrip. (b) Eye diagram homogeneous substrate vs. inhomogeneous substrate—stripline. As mentioned in [1], a stripline interconnection presents improved reflection loss compared to a microstrip interconnection and, as can be seen in Table 3, we have a reduced value for reflection loss for stripline, 68 dB, compared to 41 dB for microstrip technology in differential mode. The difference is much lower between the two technologies for common mode: 48 dB vs. 46 dB. As mentioned in [1], the number of resonance frequencies increased with the length of interconnection for both microstrip and stripline technology. As was demonstrated in the case of stripline, we had additional frequencies of resonance compared to microstrip technology: three resonances for microstrip compared to four resonances for stripline at 200 mm or four resonances vs. five resonances for 250 mm for the same technologies, as seen in Table 4.  
For a given interconnection on a PCB, we can evaluate the skew that is unintentionally induced in a differential pair due to the misalignment of conductors and glass fiber bundles in PCB substrates [37]. In [38], it was demonstrated that wider traces will see less variation of these metrics compared to narrow traces and recommended to apply the proposed numerical experiment on each case. We can also evaluate the crosstalk due to a tight separation between routes; this behavior is evaluated via S parameters, with detection of a signal from a trace to another, even if the power level is small enough. This traditional technique is widely used for electromagnetic and acoustic communications, as in [39]. Besides frequency analyses, we demonstrated that, even though the stripline technology is a more lossy medium, it does not distort the signal as much as the microstrip variant, especially with the increase of data rates. In Chapter 3, we analyzed the corresponding substrates, FR4 and N4000-13, in the time domain and showed that the traditional FR4 substrate has an increase of jitter, with an increase of frequency for both microstrip and stripline interconnections much more important compared to N4000-13. The distortion of the signal is illustrated in Figure 13a,b for microstrip at 1 GHz compared to Figure 14a,b for stripline at the same rate. With the increase of frequency, to 10 GHz, the stripline wave form and the corresponding eye diagram presents low jitter and low overshoot and undershoot, while for the microstrip lines, these parameters increase.