What is a substrate integrated waveguide and how does it compare to microstrip at the same frequency?

A substrate integrated waveguide (SIW) is a planar waveguide structure fabricated using standard PCB or LTCC technology that emulates the propagation characteristics of a rectangular metallic waveguide by using rows of metalized via holes as the sidewalls. The top and bottom copper layers of the PCB serve as the broad walls, and two rows of closely spaced vias replace the narrow walls, creating a dielectric-filled rectangular waveguide cross-section. The SIW supports the same dominant TE10 mode as a standard rectangular waveguide, with cutoff frequency f_c = c / (2 x W_eff x sqrt(Er)) where W_eff is the effective width between the via rows (slightly less than the physical via-to-via spacing due to the discrete nature of the vias). Compared to microstrip at the same frequency: SIW has lower radiation loss (the fields are fully enclosed, unlike microstrip where fringing fields radiate), SIW has higher Q factor (Q of 200-500 vs. 50-150 for microstrip at 30 GHz, making SIW better for filters), SIW has lower crosstalk and better isolation (enclosed structure prevents field coupling between adjacent circuits), SIW can handle higher power (the enclosed structure has higher breakdown voltage than the open fields of microstrip), but SIW is physically larger (the waveguide width is approximately lambda/(2 sqrt(Er)), which is larger than most microstrip circuits), and SIW has higher insertion loss per unit length than microstrip at low frequencies (due to the via losses and conductor losses on two broad walls), and SIW has a lower cutoff frequency below which it does not propagate.