Effect of ripple shape and taper on frequency response of reflectivity and transmission in a coaxial Bragg structure

By making use of the CST software, a comparative study is carried out for the effect of three ripple shapes (sinusoidal, rectangular and triangular ripples) on the frequency response in a coaxial Bragg structure. Results show that the rectangular ripple leads to the widest bandwidth while the triangular ripple narrows the bandwidth. Moreover, based on the mode-coupling model, numerical analysis is presented to demonstrate the influence of the ripple tapers. It is shown that the interval between the band gaps of the competing mode and the desired working mode is narrowed by the use of a positive taper, but is expanded if a negative taper is employed.