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105-GHz Notch Filter Design for Collective Thomson Scattering

Vedran Furtula, Poul Kerff Michelsen, Frank Leipold, Mirko Salewski, Søren Bang Korsholm, Fernando Meo, Dmitry Moseev, Stefan Kragh Nielsen, Morten Stejner, Tom Johansen

Fusion Science and Technology / Volume 59 / Number 4 / May 2011 / Pages 670-677

Technical Paper / Sixteenth Joint Workshop on Electron Cyclotron Emission and Electron Cyclotron Resonance Heating (EC-16)

A millimeter-wave notch filter with 105-GHz center frequency, >20-GHz passband coverage, and 1-GHz rejection bandwidth has been constructed. The design is based on a fundamental rectangular waveguide with cylindrical cavities coupled by narrow iris gaps, i.e., small elongated holes of negligible thickness. We use numerical simulations to study the sensitivity of the notch filter performance to changes in geometry and in material conductivity within a bandwidth of ±10 GHz. The constructed filter is tested successfully using a vector network analyzer monitoring a total bandwidth of 20 GHz. The typical insertion loss in the passband is <1.5 dB, and the attenuation in the stopband is [approximately]40 dB.

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