Abstract: A novel microstrip-to-waveguide transition is investigated in this paper, which utilizes a tramped antenna to reach its transmission characters of ultra-wide band and end-fire radiation. This monolithic-microwave integrated-circuit (MMIC)-compatible antenna is inserted in the E-plane of the rectangular waveguide to launch the TE10 dominant mode. With this new excitation scheme, compact design and low cost manufacturing are obtained without the need for multi-layer substrates or waveguide sidewall slits. Under mechanical alignment, a study shows that the designed UWB antenna coupled microstrip-to-waveguide connector has obtained return loss better than -10dB, VSWR less than 1.8 within the band (6GHz ~ 50GHz) .