**2. Geometries in presence**

**Figure 1** shows the transformation of a classical metallic rectangular waveguide (MRW) into an SIW, next into a NWSIW.

The MRW is formed by the assembly of four metallic plates acting as perfect electric conductors and forming a hollow metallic pipe of rectangular section for the guidance of electromagnetic waves.

The SIW has a fully planar thin topology since it bases on planar dielectric substrates commonly used for the fabrication of RF and microwave devices and circuits. The top and bottom faces of the substrate are covered by a metallic clad typically 17 or 35 μm-thick, as available for commercial copper clad laminates (CCL). These layers form the top and bottom walls of the waveguide. Lateral walls are obtained by

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

#### **Figure 1.**

*From metallic rectangular waveguide (MRW) to Nano-wire substrate integrated waveguide (NWSIW). In SIW lateral metal plates of MRW are replaced by two rows of metallized vias. In NWSIW rows of nanowires (NW) electrodeposited in nanoporous substrate form continuous metallic walls. Vertical arrows indicate the positioning of covering metal plates (blue).*

mechanically drilling two rows of holes that are next filled by metallic vias; periodicity and diameter of the vias must be adjusted in order to achieve a similar metallic shielding level as in an MRW.

In a NWSIW the difference with respect to SIW is the nanoporous substrate used for its design and fabrication. Instead of drilling vias in a CCL substrate, metallic nanowires (NW) are grown by electrodeposition in dedicated row areas in the nanoporous substrate in order to form a virtual metallic lateral shielding. The bottom side of the waveguide is formed by the thin metallic layer electroplated as ground electrode for the electrodeposition of NW, while top side is achieved by another electroplating realized after the growth of NW is completed.
