# Through-Wire Microstrip-to-Empty-Substrate-Integrated-Waveguide Transition at Ka-Band
## 3 Results and Discussion  
To simulate both Ku- and Ka-band transitions in CST Studio Suite, the substrate chosen was Rogers 4003C with 0.813 mm height and copper metallization of 18 \(\upmu\)m for the three layers of the transition in Ku-band, whereas in the Ka-band the same substrate was used for the bottom layer, and Rogers 4003C with 0.305 mm height and copper metallization of 18 \(\upmu\)m was chosen for the middle and top layers. Figure 2 and Table 2 show the results obtained in CST Studio Suite for the transitions designed (including the original one in the X-band for comparison) without losses, being port 1 the feeding port connected to the microstrip and port 2 the ESIW port of the transition. Comparing the results at the three frequency bands, it is possible to observe that there is a similar behavior among them with very good results in terms of insertion and return losses, and it is possible to conclude that the design method is independent of the frequency and can be applied to the design of any transition. Moreover, as it is figured out in [9], the design method allows the design for both broadband and narrowband implementations, which reinforces the robustness of the design method. \begin{table}
\begin{tabular}{c c c c} \hline  & **X-Band [9]** & **Ku-Band** & **Ka-Band** \\  & **(8.2–12.5 GHz)** & **(12–18 GHz)** & **(26.5–40 GHz)** \\ \hline \end{tabular}
\end{table} 
Table 1: Dimensions of the Three Designed Transitions in mm. Figure 1: Schematic view of the through-wire microstrip-to-ESIW transition [9]. (a) Upper layer top; (b) upper layer bottom; (c) middle layer; (d) transverse section. In order to validate the performance of the manufactured transition, the most difficult one (in the Ka-band, as manufacturing tolerances become more important) was chosen to manufacture a back-to-back structure. The same substrates as in the simulation process have been used, but since all the layers are metallized, additional copper electrodeposition of height 9 \(\upmu\)m was added to each one. The three layers have been manufactured using  
Figure 2: Simulated reflection and transmission of the microstrip to ESIW transition. **Upper–X-band** [9], **middle–**Ku-band, **bottom—**Ka-band. standard printed circuit board manufacturing processes (cutting, drilling, milling, and plating). Then they were soldered using a solder press, where the alignment of the layers is guaranteed by placing tight-fitting pins within the alignment holes. After that, the ends of the wires were manually soldered to the upper and lower layers. Figure 3 shows the layers of the manufactured back-to-back transition before assembling, and Figure 4 shows the final integrated prototype. It should be noted that at high frequency, the diameter of the filament becomes very thin, which implies that it is more difficult to manipulate. Because of this, it is recommended to use rods as straight as possible instead of cables. In this case, Ni-Ag rods were used. Moreover, as the rod has to pass throught the hole in the top and bottom covers, the metallization process should be taken into account as \(d_{hole}\) will be reduced due to the electrodeposition process being advisable to carry out some tests before the final manufacturing of the prototype to assure that rods can pass through the hole and the electrical contact is assured. More recommendations about the manufacturing process can be found in [14]. The back-to-back transition has been measured with a network analyzer Anritsu MS4644A, using a TRL calibration kit to de-embed the coaxial connectors and the microstrip line. Figure 5 shows the results obtained, with it being possible to figure out that the agreement between simulation (considering losses) and measurement results is good. Taking into account that the prototype has been manufactured in the Ka-band, differences in return losses can be due to manufacturing errors that become more important when the frequency is increased.