To solve the narrow operation-band of the electromagnetic bandgap (EBG) waveguide, a quasi transverse electromagnetic (TEM) mode waveguide using the metal-patch EBG structure as sidewall is proposed in this paper. Theoretical analysis and numerical calculation show that broader bandwidth, better transportation property, and more uniform electric field distribution of the quasi-TEM mode can be reached. Simulation results using Ansoft HFSS indicate that the metal-patch EBG structure can convert TE10 mode into quasi-TEM mode in the central frequency of 14 GHz with a bandwidth of 1.7 GHz and the uniformity of electric field distribution reaches 84.7% in 83.9% cross section area.