In this paper, we describe the development and design procedure of the new kind of coaxial TE_m,1 modes generator based on ring resonator with coupling apertures. The generator enables excitation of subsequent TE_m,1 modes in a cylindrical waveguide. The proposed design method allows to obtain high purity TE_m,1 modes. The angular mode number can be chosen by replacing the plate with coupling apertures. Structure and parameters of the generator was optimized using CST-Microwave Studio. The mode generator was fabricated and checked on the test bench in an anechoic chamber. The measured field distributions confirm excitation of the desired TE_m,1 modes. A good agreement between simulations and measurements is obtained. The presented mode generator, operating in non-rotating TE_m,1 modes, is easy to fabricate, and suitable for cold-test experiments of high power components and devices.