In this paper, we describe the design of a periodically air-filled substrate integrated waveguide (SIW) bandpass

filter in which part of the dielectric substrate is removed to reduce insertion losses. The unit cell parameters of the

structure, which are directly related to the center frequency (fc) and bandwidth (BW) of the first passband, and also to the first stopband or bandgap (BG) of the structure, have been appropriately selected for filtering purposes, thus providing some useful design rules. Furthermore, we apply the concept of glide symmetry for achieving a much larger fractional bandwidth (FBW). Additionally, a microstrip-to-SIW transition including a novel coupling iris is proposed. A prototype of the periodic SIW filter with glide symmetry has been manufactured and measured for validating purposes. The proposed filter proves to be a good candidate for millimeter wave applications.