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On the basis of ordinary sinusoidal groove structures, an auxiliary sinusoidal distribution with a smaller etching period is superimposed, and a negative-taper is added, on the inner and outer conductor walls to form a coaxial Bragg structure with tapered-double-sinusoidal grooves. Through the FORTRAN software programming simulation experiments, we can see that compared with the ordinary sinusoidal grooves, the bandwidth of the working mode and competition mode gets narrower, the quality factor Q gets greater, the residual side-lobes are also suppressed, and the selectivity of frequency is enhanced when the coaxial Bragg structure adopts the tapered-double-sinusoidal grooves. At the same time, the center resonance frequency point of the competition mode is far away from the working mode, and the bandgap overlap is further separated. However, the reflectivity of the working mode decreases and the reflectivity of the competing mode increases with the increase in the gradient angle. These peculiarities of the negative-tapered-double-sinusoidal groove structure are favorable to construct a cavity with a narrower bandwidth and high quality factor and also are favorable to the mode selectivity.

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