Abstract
A thin film is often coated on the dielectric rods used in traveling wave tubes to provide microwave attenuation. The quality of the thin film will affect the performance of the traveling wave tube. To evaluate the quality of the thin-film by measuring the attenuation performance of the dielectric rod, modified parallel strips with a sample hole are designed to provide a relatively reasonable field working environment for the attenuation evaluation. After analyzing the field distribution of the parallel strips, a sample hole is designed on the side of parallel strips, which is tangent with the outer edge of the strip. An arcuate taper is introduced into the parallel strips to reduce the impedance mismatching. Finally, two unqualified and qualified dielectric rods are measured using the modified parallel strips at frequencies 12 GHz and 18 GHz. The measured results indicate that it is feasible to evaluate whether the thin-film coated on the dielectric rod is qualified or not.
Highlights
Evaluation of the dielectric rod attenuation using the modified parallel strips that provide a relatively reasonable field environment
In the vacuum electron devices,5,6 such as traveling wave tubes (TWTs), the dielectric rod coated with carbon thin-film is a very important component for the device performance
The double ridge waveguide and the height reduced rectangular waveguide7 with a sample hole in the center can be used to measure the attenuation distribution. For both test fixtures,8–10 the E-field direction goes straightly from up to down, and this is different from the real Efield direction in TWT
Summary
Evaluation of the dielectric rod attenuation using the modified parallel strips that provide a relatively reasonable field environment. This field distribution inspired us to design a test fixture for the attenuation measurement of the dielectric rod. Another novel test fixture11 is designed to measure the attenuation distribution with higher measurement resolution, but the E-field of the parallel strips is different.
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