Microwave devices – Match each device to its typical application List I (Device) A. Reflex klystron B. Traveling-wave tube (TWT) C. Cavity klystron D. Maser List II (Application) Wideband amplification Very low power amplification (ultra-low-noise front end) Low-power FM (frequency-modulated) generation Frequency multiplication Select the correct matching between List I and List II.

Introduction / Context:
This matching problem tests core knowledge of classic microwave vacuum devices and masers. Each device has a characteristic role in RF/microwave systems—oscillation, amplification, bandwidth, noise performance, or frequency conversion. Understanding these “textbook roles” helps in system-level block diagram design.

Given Data / Assumptions:

• Reflex klystron is a single-cavity, velocity-modulated tube commonly used as a low-power microwave oscillator.
• TWT is a broadband linear amplifier based on distributed interaction.
• Cavity klystron (multi-cavity) supports amplification and can be configured for harmonic multiplication.
• Maser provides extremely low-noise, very small-signal amplification.

Concept / Approach:

Map each device to the most standard application: reflex klystron → small, tunable microwave source (often FM capable); TWT → wideband amplification; cavity klystron → narrowband high-gain amplification and also used as a frequency multiplier with harmonic extraction; maser → very low power signal amplification with exceptional noise figure.

Step-by-Step Solution:

Verification / Alternative check:

Historical and modern references consistently place TWTs in broadband amplifier chains (satcom, EW), reflex klystrons as lab signal sources, masers in deep-space or ultra-low-noise front ends, and klystrons both as amplifiers and in some multiplier roles.

Why Other Options Are Wrong:

Pairings that assign wideband amplification to klystrons or FM generation to TWTs contradict the intrinsic device physics and standard usage. Assigning “very low power amplification” to anything other than a maser ignores its defining strength.

Common Pitfalls:

Confusing reflex and cavity klystrons (oscillator vs. amplifier/multiplier) and assuming all tubes are primarily amplifiers.

Final Answer:

A-3, B-1, C-4, D-2.