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Conductor-backed slotline suffers from potential problems of mode coupling phenomenon and yields unexpected effects. Previous designs are focused on how to suppress such a mode-to-mode coupling. This unwanted coupling effect may be purposely used to achieve a desired coupling between half mode substrate integrated waveguide (HMSIW) and slotline. In this work, a hybrid HMSIW-slotline guided-wave structure is introduced and investigated. Through a simple and efficient analysis approach, we design and fabricate a 3 dB hybrid HMSIW-slotline directional coupler, which achieves a relative bandwidth of 17%~22% with 0.5 dB amplitude imbalance excited at different ports. This type of substrate integrated hybrid coupler not only presents a compact geometry, but also preserves a great design flexibility compatible with various topologies.