Circular Coaxial Filters With Organic Dielectric-Loaded for Secondary Electron Multiplication Modulation and Multipactor Verification

This article presents a systematic investigation of the surface treatment, secondary electron yield (SEY) modulation, and multipactor of two typical polymer materials used in aerospace applications: polytetrafluoroethylene (PTFE) and polyimide (PI). A wide-bandwidth low-pass circular coaxial filter with a 4.6-GHz cutoff frequency and a 1-mm discharge gap was designed to serve as a test platform for evaluating the multipactor suppression effectiveness of these materials. The wide-band capability, circular gap design, and low replication cost of this coaxial filter make it a valuable reference for coaxial multipactor research. Mechanical machining was employed to fabricate annular submillimeter grooves on PTFE and PI surfaces, lowering PTFE’s SEY maximum from 2.05 to 1.20 and PI’s SEY maximum from 1.35 to 1.15. Experimental results indicate that this surface treatment enhanced the multipactor threshold of the PTFE-filled filter from 500 to 700 W, while substantially mitigating the discharge risk in the sensitive regions of the PI-filled filter. However, the observed increase in the multipactor threshold for the PTFE-filled filter was less than predicted by simulations. Through detailed analysis of the material characterization and model development, we have identified three nonideal structural issues that have become obstacles to the effective improvement of the multipactor threshold: the SEY enhancement factor on the PTFE surface after machining, the reduced gap distance due to compression, and the decreased effective groove area. This insight is crucial for optimizing multipactor mitigation strategies for polymeric materials in aerospace applications.