Abstract: Analysis of bend waveguides shows that a small curvature-radius bend waveguide and a mitered-joint waveguide that have equal bend angles and equivalent axial lengths have similar transmission characteristics. Therefore, a new kind of TM01-TE11 11 mode converter, which is composed of several mitered-joint straight waveguides, are proposed and studied. Design method of such converters is studied, and several sample are presented, all of which have high conversion efficiencies of greater than 99% at center frequency.