Which microwave device employs a helix slow-wave structure to achieve wideband interaction with an electron beam?
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ATWT (traveling-wave tube)
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BKlystron amplifier
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CKlystron oscillator
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DBoth (a) and (b)
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EMagnetron
Answer
Correct Answer: TWT (traveling-wave tube)
Explanation
Introduction / Context:Slow-wave structures reduce the phase velocity of RF waves to interact efficiently with electron beams. Recognizing device architectures is essential in microwave engineering.
Given Data / Assumptions:
- Helix supports a slow traveling wave over a broad bandwidth.
- Electron beam interacts continuously along the helix for amplification.
Concept / Approach:The traveling-wave tube (TWT) uses a helical slow-wave structure to achieve near-constant phase velocity over a wide frequency range, enabling broad bandwidth gain. By contrast, klystrons use resonant cavities (buncher, catcher) and do not rely on a helix.
Step-by-Step Solution:
Identify devices employing helices: TWT is the standard example.Klystrons use discrete cavities and drift spaces; not helix structures.Therefore, the correct choice is TWT.Verification / Alternative check:Any microwave textbook shows cross-sections: TWT with helix winding around the beam tunnel; klystrons with cavities.
Why Other Options Are Wrong:
Klystron amplifier/oscillator: cavity-based, narrower bandwidth than helix-TWT.Magnetron: crossed-field device with resonant cavities; no helix.Common Pitfalls:
Assuming 'klystron' generically uses any slow-wave structure; only specific special designs (not standard klystrons) would.Final Answer:
TWT (traveling-wave tube)