New compact mode converters for SLAC RF pulse power compression system

A RF pulse power compression scheme has been developed at SLAC (Stanford Linear Accelerator Center) where they adopt a method of a long delay line, in an overmoded circular waveguide, to rephase the transmission mode. A low loss mode, TE₀₁ in a circular waveguide is required. However, the output mode of a megawatts klystron is a TE₁₀ mode in rectangular waveguide. A transition and mode conversion system needs to be developed. Conventional mode conversion sequence of TE₁₀, in rectangular waveguide, to TE ₀₁ mode, in circular waveguide, is using Marie´ Transition which requires very long transition length and very complicated structure. We have developed several mode converters with very compact length and high efficiency. The proposed conversion sequence is TE₁₀-TE₁₁-TE₀₁. In this sequence, our main interests are in developing the TE₁₁ and TE₀₁ uptaper, and TE₁₁-TE₀₁ serpentine mode converter at 11.4 GHz