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Due to azimuthal-asymmetric electron emitting, TE11 -mode output of high-power microwave is unavoidable in coaxial vircator. In order to obtain a pure mode output, TE11-mode enhanced design by opposed section electron emitting is applied. As 2-D effect along azimuthal direction is introduced, the frequency of microwave generated is shifted in TE11-mode enhanced coaxial vircator, compared with the thoroughly coaxial one. Frequency characteristics of TE11-mode enhanced coaxial vircator are numerically and experimentally studied by the 3-D particle-in-cell code UNIPIC. Simulation results show that a stable TE11-mode output is generated nearly with a point frequency in the S-band by TE11-mode-enhanced geometry, which is a little lower than that in the thoroughly coaxial geometry. In experiments, nearly point frequency and stable TE11-mode output is also obtained, and the effects of diode voltage, anode-cathode gap, and electron beams width are investigated. The results show that with higher diode voltage, smaller anode-cathode gap, and larger electron beam width, the microwave frequency is higher, particularly that the electron beam width has an equal effect with the diode voltage and the anode-cathode gap, which agree well with the simulation results. Meanwhile, microwave generation was obtained with steady power above 800 MW at about 5% efficiency in the experiments.