Theoretical investigation and experimental verification of compact folded substrate integrated waveguide

The folded substrate integrated waveguide (FSIW) is a more compact structure over the substrate integrated waveguide (SIW); it has almost same propagation characteristics as the SIW with 50% size reduction. The formulas of propagation and cutoff characteristics of the FSIW are derived for the first time. Good agreement is observed between the numerical simulation and the calculation results from our formulas. The measured results of prototypes are found to agree with the numerical simulation results, further demonstrating the validity of the theoretical analyses.