Design of wide-band mode discriminator based on mode-selective coupling

With instantaneous and in situ characteristics, mode discriminators based on mode-selective coupling principles attract much attention, but their working bandwidth is restricted by the distribution of the equal distance between adjacent holes and the equal radius of all holes. Meanwhile, the equal-interval and unequal-radius distribution of holes can increase the bandwidth of the mode discriminators remarkably. Therefore, the basic theory, designing method and example of the mode discriminators based on the equal-interval and unequal-intensity (i.e. various radii of holes) coupling are brought forward in this paper. The formulas of coupling intensity in terms of binomial distribution and Chebyshev distribution are also presented. The calculation shows that the working bandwidth of the mode discriminators based upon mode-selective coupling according to binomial distribution or Chebyshev distribution can reach 15% to 19%, which is twice over that of equal-interval and equal-intensity coupling mode discrimin...