“…The substrate integrated waveguide (SIW) [2] and the substrate integrated coaxial line (SICL) [3] are two proposals of substrate integrated circuits that have been a great advance in this field. Several passive components developed in these technologies, including filters [4,5], ultra-wideband filters [6,7], antennas [8,9], transitions and tapers [10,11], baluns [12,13], couplers [14,15], power dividers [16], and new transmission lines [3,[17][18][19][20], have been proposed. However, although their quality factor and losses are better than those of the planar circuits, these characteristics can be further improved (without losing their compactness and low-cost manufacturing) if the dielectric substrate is removed and the waves are allowed to propagate through the air.…”