This document outlines intermodulation distortion measurements for power amplifiers, specifically focusing on the characterization of a traveling wave tube (TWT) amplifier using the PNA N5225A. It details procedures for S-parameters, AM/AM, and AM/PM measurements as well as calibration techniques necessary for accurate results. Additionally, the document describes two-tone test configurations for assessing amplifier performance.

1. PA Intermodulation Distortion
Measurements Using the PNA
María Jesús Cañavate Sánchez

2. Index
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1. Introduction: characterization of a power amplifier
2. PNA N5225A
3. S-Parameters
4. AM/AM
5. AM/PM
6. Two-tone test

3. 1. Introduction: characterization of a
power amplifier
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S-Parameters
DUT: Amplifier

4. 1. Introduction: characterization of a
power amplifier
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Nonlinear characteristic
AM/AM and AM/PM compression
of a typical Traveling Wave Tube
(TWT) amplifier.

5. 1. Introduction: characterization of a
power amplifier
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Intermodulation distortion
DUT: Amplifier
Frequency spectrum of the amplifier
input signal: 5 unmodulated carriers.
AM/AM and AM/PM compression
of a typical Traveling Wave Tube
(TWT) amplifier.
Frequency spectrum of the amplifier
output signal: 5 unmodulated
carriers and IMP3.

6. 2. PNA N5225A
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- Number of ports: 4
- Frequency range: 10MHz – 50GHz
- Max. port power, 20GHz: +13dBm
- Receiver damage level: +15dBm

7. 2. PNA N5225A
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Damage: +15dBm
Damage: +30dBm
Damage: +43dBm
Coupling factor: 15dB

8. 3. S-Parameters
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Power flow analysis (for all types of PA measurements)

9. 3. S-Parameters
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Before calibration: make sure settings are at desired levels

10. 3. S-Parameters
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Select power and internal attenuators levels
- Output power: -10 dBm
- Gain: 26 dB
- External attenuation: 6 dB
- Internal attenuation: 15 dB
- Measured S21 drops by the attenuation
- After calibration, attenuator losses will
be removed
- Before calibration: Gain = 5 dB
- After calibration: Gain = 26 dB
- Internal attenuation still not available

11. 3. S-Parameters
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Calibration performance (for all types of PA measurements)
 Source–power calibration at the input point of the amplifier
 To ensure a constant and known power
 Material needed: power sensor
 Two-port SOLT calibration
 To remove effects of the external and internal attenuators
 Material needed: mechanical calibration kit
 SOLT: short-open-load-through

12. 3. S-Parameters
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Calibration performance
Source–power calibration Two-port calibration

13. 3. S-Parameters
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Measurements

14. 4. AM/AM
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S21 measurement under a power sweep condition
- Attenuator settings are fixed
- Source-power calibration at
source and receiver ports

15. 4. AM/AM
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S21 measurement example
Gain
AM/AM

16. 5. AM/PM
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Procedure:
 S21 measurement under a power sweep condition
(AM/AM).
 Change the S21 measurement from log magnitude format
to phase format.
 No new calibration is required.

17. 6. Two-tone test
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2 different configurations (option 087):
 Using internal PNA components
 Only extra cables are required
 Using external components
 Combiner
 Coupler
 Extra cables

18. 6. Two-tone test
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Using internal PNA components:

19. 6. Two-tone test
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Using external components:

20. 6. Two-tone test
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21. 6. Two-tone test
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Frequency tab:

22. 6. Two-tone test
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Power tab:

23. Thank you!
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PhD student: María Jesús Cañavate Sánchez // mjc31@hw.ac.uk