This document discusses key considerations for characterizing electromagnetic interference (EMI) probes. It analyzes examples of probe characterization data and identifies potential issues. Specifically, the document emphasizes that characterization should: (1) provide unwanted field rejection data to determine usable frequency range, (2) demonstrate lower frequency performance in a practical setup, and (3) use proportional scaling and logarithmic frequency axes for evaluation. Without such details, the document asserts that characterization data is insufficient to properly evaluate a probe's specifications and performance.

1. Probe Characterization
Amber Precision Instruments, Inc. (API)
Jul. 23, 2014

2. Our EMI Probes
1
EMI Probes:
- Up to 6 GHz
- Up to 20 GHz
- Up to 40 GHz
Optional EMI Probes;
Choose:
- Size
- Frequency range
- Field Component
* EMI Hx 2 mm

3. Characterization Structure
up to 15 GHz
2
50 Ohms Microstrip Line (MSL)

4. Characterization Structure
up to 40 GHz
3
50 Ohms Air-Dielectric* Coplanar Waveguide (CPW)
* To avoid the effect of non-TEM waves on probe characterization at higher freqs (>15 GHz).

5. Probe Characterization Setup
4

6. Typical EMI Probe S21
5
1 2 3 4 5 6 7 8 9 10
x 10
9
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
* EMI Hx 2 mm: up to 10 GHz

7. What Are the Specs?
6
10
8
10
9
10
10
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
10
8
10
9
10
10
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
20 dB/dec Line
Log freq: Low freq with 20 dB/dec slope
* EMI Hx 2 mm

8. What Are the Specs?
7
High freq: How high the probe measures?
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 10
10
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
* EMI Hx 2 mm

9. What Are the Specs?
8
10
8
10
9
10
10
-100
-90
-80
-70
-60
-50
-40
-30
Frequency [Hz]
|S21|[dB]
Hx Field,  = 0
Unwanted Field,  = 90
Unwanted field: Decoupling of unwanted components
* EMI Hx 2 mm

10. What Are the Specs?
9
10
8
10
9
10
10
-65
-60
-55
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
10
7
10
8
10
9
10
10
-90
-80
-70
-60
-50
-40
-30
Frequency [Hz]
|S21|[dB]
Low freq: How low the probe measures
in a “practical” setup?
20 dB/dec slope
60 dB dynamic range
4 MHz

11. High Freq Probe
10
10
9
10
10
-90
-80
-70
-60
-50
-40
-30
Frequency [Hz]
|S21|[dB]
Hx Field,  = 0
Unwanted Field,  = 90
* EMI Hx 1 mm L: up to 20 GHz

12. Probe Factor
11* EMI Hx 2 mm
10
8
10
9
10
10
20
30
40
50
Frequency [Hz]
|PF|[dB(A/m)/V]
Measured Probe Factor
Theoretical Open-Circuit Probe Factor
Probe factor: Provide probe factor
SmartScan imports probe factor
SmartScan measures and calculates system factor

13. Other Methods of
Data Presentation
• How other people characterize their probes?
• How the characterization data is presented?
• Is their data presentation fair?
12

14. Example* of 10 kHz (?) to 6 GHz
Probe Data Presentation
13
Let’s analyze the data!
Extract
* Aprel: http://media.wix.com/ugd/36d46a_46d2902bfdd24c25b401582e6a488370.pdf

15. Is Freq Scale OK?
14
Why the freq axis of
extracted data don’t
match?!
Let’s see!
Let’s analyze the data!

16. Is Freq Scale OK?
15
0.99999 GHz 1.3 GHz 1.3 GHz 1.3 GHz 1.1 GHz
Why all ticks are
equal?!
Well, not a big deal.
Maybe just a typo!

17. Lower Frequencies
16
Why all ticks are
equal?!
Well, not a big deal.
Maybe just a typo!
What happened to
lower freqs?!
Is it extrapolated or
really measured?
What is the measurement
instrument setup (IF BW,
span, no. of points, etc.) to
measure down to 10 kHz?
Is it a “practical” setup?

18. Plot It Differently
17
10
4
10
5
10
6
10
7
10
8
10
9
-120
-100
-80
-60
-40
Frequency [Hz]
|S21|[dB]
What if we plot it
in a different way
(log freq)?
10
4
10
5
10
6
10
7
10
8
10
9
-120
-100
-80
-60
-40
Frequency [Hz]
|S21|[dB]
20 dB/dec Line
The probe is NOT
purely inductive
at lower freqs
(as claimed).
Is it probe issue?
Or, measurement
issue?
Or, simply not
extrapolated the
right way?
Note: Simple extrapolation
(even if it is done the right
way) does NOT mean probe
can measure down to that
freq!

19. How about 10 kHz to
20 GHz (?) Probe?
18
Extract
Let’s analyze the data!

20. Flat Response (?)
19
Let’s analyze the data!
The data is from -30 dB
to -60 dB. Why the scale
is from 0 to -180 dB?!
Well, it looks better* this
way! :-)
*“flat response across
the frequency range”

21. Plot It Differently
20
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
x 10
10
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
What if we plot it
in a different way
(tight scale)?

22. Plot It Differently
21
What if we plot it
in a different way
(log freq)?
10
8
10
9
10
10
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
10
8
10
9
10
10
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
20 dB/dec Line
The lower freqs seems
to be fine for this prob.
The deviation might be
just data extraction
error.

23. 10
8
10
9
10
10
-50
-45
-40
-35
-30
Frequency [Hz]
|S21|[dB]
20 dB/dec Line
Higher Frequencies
22
How about the
higher freqs?
There is about
20 dB notch @
13 GHz!
A deep notch is usually
a BIG red flag for
“unwanted field” coupling!

24. Higher Frequencies
23
The question is:
How to make sure this probe
measures the “desired field”
up to 20 GHz (as claimed)?
The “unwanted field” decoupling
data of probe need to be provided.
This probe is suspected
to work <10 GHz,
unless the rejection info
is available!

25. 10 kHz to 40 GHz Probe
24
Let’s analyze the data!
Extract

26. Flat Response (?)
25
Let’s analyze the data!
Same question:
The data is from -35 dB
to -55 dB. Why the scale
is from 0 to -120 dB?!

27. Plot It Differently
Single Probe Solution (?)
26
What if we plot it
in a different way
(tight scale and
log freq)?
10
10.2
10
10.3
10
10.4
10
10.5
10
10.6
-50
-45
-40
-35
Frequency [Hz]
|S21|[dB]
This info is NOT sufficient
to evaluate the probe up
to 40 GHz!
The “unwanted field” decoupling
data of probe need to be provided.
What does happen to lower freqs?
Does this probe have sufficient
sensitivity to measure down to 10
kHz?!

28. Another Example* of Data
Presentation
27* Detectus AB: http://www.detectus.se/products_nearfieldprobes.html
Again, the data is from -30 dB
to -60 dB. Why the scale is
from 0 to -60 dB?!
Without unwanted field data,
there is no sufficient info to
evaluate the probe.
Log freq scale is required for
low freq evaluation.

29. What to Look for in
Probe Characterization Data?
• Unwanted field rejection data need to be provided to
determine higher usable freq.
• Is lower usable freq achievable in a “practical” setup?
• Is the probe purely inductive/capacitive at lower freqs?
• Is the characterization structure (MSL, CPW, etc.) suitable for
freq of interest?
• What is the measurement setup/condition?
• Is the scale proportional to data range?
28

30. 29
Questions?
Contact us: amberpi@amberpi.com
www.amberpi.com