RF design and test of a high-directivity high-power waveguide directional coupler for the HEPS

Purpose A novel high-directivity high-power waveguide directional coupler (DC) working at 2998.8 MHz is developed for the HighEnergy Photon Source. It can help the phase control system to obtain a very accurate microwave signal, which is very importantto minimize the beam emittance.
Methods The novel reversely placed T-type coupling piece helps to obtain a high directivity. The N-type high-vacuumfeedthroughs for vacuum sealing instead of the traditional ceramic plate is beneficial to holding a higher peak power. Thesimulation and the high-power commissioning are accomplished in the Institute of High Energy Physics (IHEP), while thefabrication and the low-power test are conducted in cooperation with the manufacturer.
Results Both the single-coupler and the dual-coupler DCs are developed with a directivity of more than 35 dB while keeping thecoupling factor within 60±0.5 dB. Finally, 69.4 % of all the fifty-two mass produced DCs have got a directivity of more than 40 dB.Conclusion: The mature manufacturing process for mass production is obtained. The novel high-directivity high-power waveguideDC can be mass produced with an actually internationally leading performance.