Design Optimization of Prototyped 1.3GHz/14kW Input Coupler: A Simulation Study

The prototyped 1.3 GHz/14 kW input-coupler was designed via CST simulation,to couple the hard X-ray free-electron laser-beam for Shanghai Light Source(SSRF) project.The newly-designed coupler mainly comprises the cold/warm assemblies,waveguide-to-coaxial transition adaptor and inner conductor adjustment drive.The ceramic cylinder in cold(warm) assembly maintains UHV-condition; depending on the coupling degree and/or beam load,the antenna penetration depth into the cavity can be regulated by adjusting bellows' lengths.In rectangular to coaxial waveguide transition,the waveguide-to-coaxial transition adaptor converted TE₁₀ mode into TEM mode.The simulated results show that the new prototyped coupler meets the design requirements.For instance,operating at 1.3 GHz/14 kW,the power transmission coefficient S₁₁ was-24.73 dB; meanwhile,when it comes to newly-optimized rectangular waveguide connected to the coupler,S₁₁ was-47.29 dB at 1.3 GHz,and the bandwidth was 118 MHz for an S₁₁ below-20 dB.