# Efficient Implementation of Polymer Microwave Fiber Links Employing Non-Galvanic Coupling Mechanism
## 5 Conclusions  
PMF links offer a very good solution for medium-distance, high-data-rate links at sub-THz. By utilizing low-loss polymer materials, attenuation as low as 1 dB/m is possible. Additionally, the simulation results show that multimode operation not only does not worsen the overall group delay and thus the performance of the link, but it benefits the coupling, as a PMF with larger cross-section can be utilized, as long as the higher-order modes are suppressed, as illustrated in this paper. The modal and waveguide dispersion is optimized through the correct sizing of the PMF in the desired frequency of operation. However, dispersion compensation can be further implemented in the digital domain of the system [31] using our proposed design. In terms of the coupling mechanism, the link's flexibility offers a variety of coupling solutions that can be utilized. The less complex and cost-efficient antenna-in-package that we propose achieves an average coupling loss of 3.5 dB. An important factor that is not covered in this paper is the temperature. Regarding eWLB structures, the temperature will not reduce the links' performance as presented in [29; 30]. On the other hand, the PMF will be the bottleneck of the link in terms of the temperature impact. However, there are polymer materials available that can support high temperatures while presenting similar dielectric performance [24]. As a last remark, the eWLB technology enables the scalability of the proposed design to lower frequencies, making it a viable solution for a wide range of applications. A notable example is presented in [29], where the concept of an eWLB package-integrated circularly polarized antennas in the 57 GHz to 64 GHz ISM band is introduced. Additionally, in [30], various eWLB package-integrated antennas are introduced operating at 77 GHz, including a similar Vivaldi antenna to that presented in this paper. This scalability not only facilitates adaptation to different frequency bands but also enhances the potential for integration into future radar and communication systems, driving further advancements in the field. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ref.** & **Coupling Type** &
\begin{tabular}{c} **Frequency** \\ **(GHz)** \\ \end{tabular} & **Implementation** & **Coupling Loss (dB)** \\ \hline
[8] & Wireless & 60 & On-Chip Antenna & 6 (simulated) \\ \hline
[9] & Wireless & 120 & On-Chip Antenna & 11 (measured) \\ \hline
[11] & Wireless & 120 & On-Chip Antenna & 7.1 (simulated) \\ \hline
[10] & MMIC interface & 120 & PCB & 3.4 (measured) \\ \hline
[12] & Wireless & 140 & PCB & 3.5 (measured) \\ \hline
[16] & Wireless & 130 & Antenna-In-Package & 3 (measured) \\ \hline This work & Wireless & 140 & Antenna-In-Package & 3.5 (measured) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Proposed coupler’s performance against the literature. **Author Contributions:** Conceptualization, V.L., M.W. and W.H. ; Methodology, V.L. and Y.P. ; Formal analysis, V.L. ; Investigation, V.L. ; Resources, Y.P. ; Writing--original draft, V.L. ; Writing--review & editing, Y.P. ; Visualization, W.H. ; Supervision, Y.P. ; Project administration, Y.P., F.D. and M.W. ; Funding acquisition, F.D. All authors have read and agreed to the published version of the manuscript. **Funding:** This work was partially funded by the H2020-ICT-07-2018 Project No. 824962 \"Car2 TERA\". Part of this work was funded by the European Union's Horizon Europe program under grant agreement No. 101096302 (6 GTandem). The 6 GTandem project has received funding from the European Union's Smart Networks and Services Joint Undertaking (SNS JU). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author. **Conflicts of Interest:** [PERSON], [PERSON] and [PERSON] were employed by the company Infineon Technologies AG.