Air-SIW Unit Cell with Glide-Symmetric Structures

This paper presents an air-SIW unit cell which is composed of contactless unit cells and periodic structures that modify the phase constant. The contactless unit cells are located on both sides of the waveguide to confine the propagating field into the air-SIW. The proposed unit cell which has a doublemushroom with off-center via generates a stopband between 26.5 GHz and 473 GHz up to a gap size of 0.1 mm. Two types of elements which modify the phase constant in the air-SIW unit cell have been analyzed. First, three slots on both broad sides of the waveguide are introduced, and later, single -mushrooms. The application of glide symmetry to theses elements are studied. Glide symmetry produces a larger operating bandwidth while maintaining linearity in the phase constant and producing a phase shift of 32 degrees in 3.9 mm length at 40 GHz regarding an air-SIW unit cell without periodic structures.