# LDS Realization of High-Q SIW Millimeter Wave Filters with Cyclo-Olefin Polymers
## 5 Conclusions  
In conclusion, through the presentation of very acceptable experimental electrical responses, we have demonstrated that high quality factor filters can be fabricated on COP substrates through a cost efficient and robust process, combining molding, machining and laser direct structuring for metallization. To provide an adequate demonstration, we chose to work with high order narrow-band filters in the millimeter wave range. Under these conditions, we approach the limits in terms of sensitivity. Indeed, we cumulated the tolerances of all the steps of fabrication. However, even at millimetric frequencies, the discrepancy between simulations and measurements is slight, and can be significantly minimized by a better knowledge of the permittivity of the polymer. If necessary, tuning elements could be added on each cavity. The process applied here for a millimeter wave miniature circuit is obviously applicable for real 3D devices presenting higher reliefs, and in the centimetric frequency range where the devices are larger and where the frequency shift would be negligible.  
Compared to standard ceramic substrates, which are not easy to machine, COP offer the possibility of building 3-dimensional shapes that can satisfy both electrical constraints and interconnection compatibility with the other components in a complex system. In terms of loss tangent, COP are comparable to ceramics usually used in RF. Since the size is not a problem in high frequency, its low permittivity is an advantage for limiting the sensitivity of fabrication tolerance. Moreover, it is a low-cost material, well suited for mass production, and is thus perfectly suited to the chosen fabrication processes.  
In terms of genericity we have designed a specific transition usable with different filters. We have also shown that a mold can be used for several different filters, which is another advantage with regard to cost considerations. Fabrication could be improved by choosing other metallization processes, such as inkjet, which would allow the use of COP not compatible with LDS, hence offering better characteristics in terms of loss tangent.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref**} & **Material** & **Footprint** & **Height** & **Volume** & **Order** & **F0** & **BW@3 dB** & **IL** & **Q** & & **Access Line** & \\ \cline{2-11}  & **-** & **mm2** & **um** & **mm2** & **-** & **GHz** & **\%** & **dB** & **-** & **Configuration** & **Height** & **Size (mm)** \\ \hline
[7] & ROS880 & 242 & 508 & 122 & 6 & 35 & 5 & 2 & 260 & CPW & 0.508 & w + 2s = 1.66 \\ This ref & COC (filter 1) & 200 & 1300 & 260 & 6 & 37.5 & 7 & 1.4 & 266 & Microstrip & 0.3 & W = 0.9 \\ This ref & COC (filter 2) & 200 & 1300 & 260 & 6 & 37.5 & 4 & 2.2 & 296 & Microstrip & 0.3 & W = 0.9 \\
[8] & ROS880 & 65 & 1106 & 72 & 6 & 82.6 & 7.2 & 2.5 & 145 & Aperture & 1.106 & 1.01 \(\times\) 1.71 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison with other solutions.  
Figure 11: Surface roughness of the metallization observed under an optical microscope.  
As the cost is one of the advantages of the fabrication process associated with this material, possible applications could be found in several domains where large series are needed: Radio front ends for Internet of Things, payload of satellite constellations, etc.  
The presented work was carried out in collaboration of all authors.  
This work was funded by the direction Generale de l'Armement (DGA) under the frame of a French Research Agency (ANR) project ASTRID 2012 COCORICO.  
The authors would like to thank the Centre Technique Industriel de la Plasturgie et des Composites, IPC Oyonnax, France, for manufacturing the prototypes.  
The authors declare no conflicts of interest.