Modified Corrugation-Based W-Band Waveguide With Selective Notched Operation for Fusion Plasma Diagnostics

Instrumentation used in the diagnostic of signals in fusion experiment needs protection against surges in signal power, which emerges from the electron cyclotron resonance heating (ECRH). In this article, a design methodology for the development of selective single notch waveguide is presented. The design of the notch filter is a circular corrugated waveguide that has been modeled based on the second-order Bragg-resonance condition. The device operation is between 75 and 105 GHz (i.e., W-band), and a single stopband frequency is achieved. The magnitude of stopband transmission is further improved by modifying the corrugation geometry, where selected corrugations are combined periodically inside the waveguide. The proposed design allows the propagation of HE₁₁ mode. Due to the Bragg condition, the LP₁₂ mode is observed at the frequency of stopband resonance, i.e., 94 GHz. The proposed device was fabricated, and the measured transmission coefficient (S₂₁) was observed in coherence with the simulated S₂₁ profile. The notch filter finds an important application in wideband signal diagnostics of electron cyclotron emission (ECE) and reflectometry in the fusion plasma experiments.