Dispersion relation of tapered MILO

The tapered coaxial slow-wave-structure is the most important part of a MILO. According to the Maxwell equations and Floquet’s theorem, the dispersion function of TM modes in the tapered MILO is derived in this paper. Through numerical calculation, the influences of several structure parameters on the dispersion characteristics are summarized, which provide some theoretical fundamental to the design of the tapered MILO.