Safe RF power measurement chain for a 2 kW TWT amplifier — choose correct connection order Components available: (1) TWT amplifier (2 kW output), (2) Low-pass/High-pass filter, (3) Low-power 20 dB attenuator, (4) 40 dB directional coupler with matched load on the through line, (5) Power meter. What is the correct sequence from source to meter?

Introduction / Context:
Measuring the output power of a high-power traveling-wave tube (TWT) amplifier requires a chain that both protects low-power instruments and provides a representative sample of the fundamental signal. The right order prevents damage and ensures accuracy.

Given Data / Assumptions:

• TWT output power ≈ 2 kW (dangerous for small components).
• Available parts: filter, 40 dB coupler, 20 dB attenuator, power meter.
• Directional coupler is assumed to be high-power rated on the main line.

Concept / Approach:
First, place the harmonic-conditioning filter directly after the TWT so the sampled signal represents the fundamental and to keep out-of-band energy from the measurement path. Next, use the high-power directional coupler on the main line; its coupled port extracts a small, known fraction (e.g., −40 dB) of the forward power. Then, because even the coupled power from 2 kW can still be substantial, insert a low-power 20 dB attenuator in the sample path before feeding the power meter. Finally, terminate the through line properly with the matched load or the system under test.

Step-by-Step Solution:

Verification / Alternative check:
With 2 kW (≈ 63 dBm), a −40 dB coupler gives ~23 dBm at the coupled port; adding −20 dB attenuation gives ~3 dBm to the meter, well within many sensors’ ranges.

Why Other Options Are Wrong:

• A/D: Sampling before filtering yields a measurement polluted by harmonics and may stress the coupler differently.
• B: Placing a low-power attenuator directly after a 2 kW TWT risks immediate damage.

Common Pitfalls:
Connecting the low-power attenuator on the main line; omitting the filter so the meter over-reads due to harmonics.

Final Answer:
1, 2, 4, 3, 5