Tunable Waveguide Notch Filter for Plasma Diagnostics

A design of a tunable notch filter based on prismatic and pyramidal resonators is proposed. In Ka frequency band, two samples of the filter with a prismatic resonator were manufactured, one of them by mechanical processing, and another using polymer 3D printing technology, followed by surface metallization. A good agreement was shown between simulated and measured characteristics of the fabricated filter samples, including a 20% stopband tuning. The attenuation of the single-cavity Ka band notch filter at the central frequency of stopband was -25 dB. Numerical simulations showed that when the number of resonators is increased to four, the attenuation increased to -60 dB in the absence of parasitic stopbands in the frequency range from 26 to 47 GHz. For a three-cavity filter with a pyramidal cavity in the numerical simulation, attenuation of -92 dB at a frequency of 240 GHz was obtained, which makes this filter attractive for plasma diagnostics systems in a promising prototype of an industrial fusion reactor of the next generation (DEMO).