**6. Challenges and perspectives of the new NWSIW technology**

Coming to the end of this chapter, it is now time to conclude on the performances, the maturity and the perspectives of the NWSIW technology.

The NWSIW presented in this chapter and the classical planar SIW of **Figure 1** share about the same pros and cons:

	- The resulting disadvantage is that both topologies require specific matching structures to solve the impedance mismatch issue resulting from the low thickness of the substrate.
	- However, the issue disappears if a whole architecture of devices is built in the same NWSIW technology on a single AAO substrate. The design can be made for a same reference impedance, so that a single transition will be needed for


#### **Table 3.**

*Comparison of insertion loss.*

interfacing the designed circuit in NWSIW technology with 50 Ω reference impedance.

	- For classical SIW, vias have to be carefully dimensioned and spaced in order to induce an efficient shield.
	- while for NWSIW a thin wall of grown nanowires is sufficient to form an efficient shield, since the nanoporous AAO template imposes a close packing of the electrodeposited MNW array.
	- This reduces the size of the device for a given operational frequency
	- Devices have to cope with dielectric loss of the substrate filling the waveguide.

However, the insertion losses observed in **Figure 11** for NWSIW (8 dB at 12 GHz, corresponding to 4.4 dB/cm) are comparable or lower than other technologies/topologies, as shown **Table 3**. Insertion losses should be significantly decreased by further improvement of fabrication process. Indeed, the upper and lower Cu layers electroplated on the two faces of the AAO membrane can be thickened in order to attenuate the effect of the roughness of the metallization due its imperfect contact with porous template during step 1 and 5 of the fabrication (**Figure 10**). This will increase the shielding effect while reducing ohmic losses, in order to achieve insertion losses lower than 1 dB/cm.

The road to achieving these objectives is not actually that long. We have shown that the combination of nanowires and SIW technologies is meaningful, since it allows a facile integration of various functionalities such as filtering and nonreciprocity on a same substrate thanks to the growth of various kinds of MNW in AAO while tuning

*Challenges and Perspectives for SIW Hybrid Structures Combining Nanowires and Porous… DOI: http://dx.doi.org/10.5772/intechopen.105148*

their filling height. The fabrication of a platform of miniaturized NWSIW devices that rival the state-of-the-art will be made possible by some optimizations of the fabrication process as outlined above.
