# Efficient Implementation of Polymer Microwave Fiber Links Employing Non-Galvanic Coupling Mechanism
## 4 AiP Implementation and Measurements
### Coupler Measurement  
To evaluate the antenna-coupler performance, a back-to-back antenna setup was designed and fabricated in order to simplify the hardware needed for the measurements. For the antenna's integration in the eWLB packaging technology, large metal areas were not allowed. For this reason, we introduced holes in the metal through cheesing. It is noteworthy that cheesing did not affect the antenna's performance. In Figure 22a, a photo of the back-to-back antennas is illustrated. The two antennas are connected through a 6 mm dual coplanar strip line. The concept of this design is to utilize two PMFs, which are connected to a VNA port each, and feed the antennas through their other side, as illustrated in Figure 22b.  
The coupling losses for a single antenna can then be easily calculated from the measured \(\left|S_{21}\right|\) of the structure as follows:  
\[\text{Cp.Loss}=[\left|S_{21}\right|-(\text{CPS Loss})-2*(\text{PMF Loss})]/2 \tag{5}\]  
At this point, it is important to mention again that the Vivaldi antenna suppresses the electromagnetic waves with electric fields perpendicular to its plane. However, such a field is produced by the extenders and is guided along the PMF, as shown in Figure 23. For this reason, the plane of the antenna needs to be parallel to the electric field of the extender and perpendicular to the plane of the working bench, as shown in Figure 24 on the right.  
Figure 21: Simulated and measured \(\left|\text{S21}\right|\) at 1 m.  
Figure 22: (**a**) Microscopic view of the back-to-back antennas and (**b**) measurement setup model in HFSS.  
For the antenna coupling measurements, 20-cm-long PMFs were used and carefully aligned with the antennas on the eWLB. As shown in Figure 25a, a good match between the measurements and simulations was obtained. Using Equation (5), the antenna coupling losses were calculated, as shown in Figure 25b.  
At lower frequencies, low coupling loss is observed. This is a result of the weaker field confinement of the PMF, which leads to extra coupling between the two PMFs without the  
Figure 23: E-field of the extender module.  
Figure 24: Antenna placement for measurement at 90 deg (**left**) and 0 deg (**right**).  
Figure 25: (**a**) \(|\)S211 of the back-to-back antenna structure, (**b**) antenna coupling losses and (**c**) \(|\)S211 of the back-to-back antenna structure rotated by 90 degrees.  
antenna. However, when rotating the antenna at 90 deg (Figure 24, left), the suppression of the electromagnetic field is observed through the much lower \(\left|\text{S21}\right|\) of the structure, as shown in Figure 25c. This proves that the coupling is mainly due to the antennas and not to power transfer over the air around the two PMF sections.  
In conclusion, the proposed structure offers a very cost-efficient and robust solution with relatively low coupling loss (approximately 3.5 dB), while it presents high displacement tolerance. Its mechanical stability and high level of integration will be beneficial for many real-life applications.  
A comparison between the state-of-the-art IC-PMF coupling solutions is shown in Table 2.