Slab Air-Filled Substrate Integrated Waveguide

The slab air-filled substrate integrated waveguide (SAFSIW) is presented as a compromise between the high performance air-filled substrate integrated waveguide (AFSIW) and low profile dielectric-filled substrate integrated waveguide (DFSIW). Both theoretical and experimental studies are presented in order to investigate SAFSIW structures. To the authors' best knowledge, this is the first time that an SAFSIW-to-DFSIW transition is reported. A 90° phase shifter based on SAFSIW and a patent pending mounting process is also introduced. Measured results show a very high figure of merit (FoM) over the Ka-band. A phase difference of $\mathbf{86}\pm \mathbf{5}.\mathbf{4}^{\pmb{\circ}}$, an amplitude imbalance of $\mathbf{0}.\mathbf{05}\pm \mathbf{0}.\mathbf{15}\ \mathbf{dB}$ and a FoM of $\mathbf{457}^{\pmb{\circ}}/\mathbf{dB}$ are obtained.