In this paper, a novel patent pending air-filled substrate integrated waveguide (AFSIW) Y-junction circulator topology intended for high-power handling space applications is presented. This new device has been developed to pave the way for future implementation of compact high-power microwave systems on substrate (SoS) based on the low-cost and high-performance AFSIW technological platform. This new circulator structure takes advantage of the AFSIW multilayer feature. It is not based on any impedance matching metal post or dielectric spacer. Instead, for matching purposes, the AFSIW top substrate material is used to load a full-height ferrite loaded Y-junction. This simple arrangement provides ease of manufacturing together with a high continuous wave (CW) and multipactor power handling capability, as the ferrite surface can be increased thank to sufficient design latitude and no gap is involved, respectively. For experimental validation, a demonstrator operating at 18.65 GHz, within the satellite downlink Ka-band, is designed and manufactured. It achieves a return loss, transmission loss, isolation and multipactor power handling in a fault short-circuited configuration of 20 dB, 0.68 dB, 21 dB and better than 200 W, respectively.