A Tri-band Serpentine Mode Converter Applied in High Power Microwave

In this paper, a tri-band serpentine mode converter applied in high power microwave is proposed. This mode converter consists of an outer coaxial waveguide and an inner embedding circular waveguide, and they have the same curvature distribution along longitudinal propagation axis. The outer coaxial mode converter operates at 8.5 GHz (X band) and 15 GHz (Ku band), the center frequency of the circular mode converter is 35 GHz (Ka band). In the mode converter, the injected coaxial TEM mode (coa.TEM) and circular TM 01 modes $\mathrm{(cir.}\mathrm{TM}_{01})$ can be transformed simultaneously into coaxial and circular TE 11 modes (coa. $\mathrm{TE}_{11}$ and cir, $\mathrm{TE}_{11})$ , respectively. The results validated by CST show that the maximum conversion efficiencies of the synthesized mode converter at central frequencies are all over 97.8%, and the bandwidths (conversion efficiency is over 95%) are 730 MHz, 820 MHz, and 720 MHz, respectively.