This document discusses using a vector network analyzer (VNA) for signal integrity testing. It begins with an overview of RF connectors and their impact on measurement accuracy. It then describes how a VNA works, measuring both amplitude and phase to determine S-parameters. Key aspects covered include calibration to define a reference plane, measuring transmission and reflection parameters, and converting frequency domain data to the time domain. Applications discussed include time domain reflectometry for fault detection and measuring rise times.

1. 1
Signal Integrity Testing
with a Vector Network Analyzer
Neil Jarvis
Applications Engineer

2. Agenda
 RF Connectors
 A significant factor in repeatability
and accuracy
 Selecting the best of several types
for application
 Compatibility
 Connectors are consumables
 limited lifetime
 damaged connectors are costly
 proper care maximizes lifetime
 VNA
 What is a Vector Network
Analyzer?
 How will a VNA help with Signal
Integrity?
 Calibrating and (De)Embedding
 What is TDR?
 The VNA approach to TDR

3. Connector Considerations

A significant factor in repeatability and accuracy

Selecting the best of several types for application

Compatibility

Connectors are consumables
o limited lifetime
o damaged connectors are costly
o proper care maximizes lifetime

4. Amplitude and Phase Error from VSWR
 εA = 20 * log (1 ± |ΓA * ΓB|) dB
 εΦ = (180 / π) *| ΓA| * |ΓB|

5. Performance of a standard type-N connector

6. Performance of a mated pair SMA vs. 3.5 mm
-Introduction
-Detailed Views
-RF Connector Types
-Connector Grades
-Comparison of SMA and 3.5mm
-Connector Summary
-Cleaning

7. Mating SMA with 3.5 mm
SMA/SMA
Conventional
Mated Pair
3.5mm/SMA
Conventional
Junction
FREQUENCY in GHz
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1.05
1.10
1.15
SWR
3.5mm
Mated
Pair

8. Performance of a mated pair 2.92 mm vs. 3.5 mm

9. Typical Connector Cross Section
Male Female
Center
Conductor
Outer
Conductor

10. Outer Conductors
Outer conductor mating surfaces define
measurement reference plane

11. Center Conductors

12. Slotted Female Center

13. Slotless Female Center Conductor

14. Connector Grades
 Metrology
 Instrument
 Production (Field)

15. Metrology Grade

Used on calibration standards

Highest performance slotless contacts

Tightest tolerances

Air dielectric interface

Long life

Highest cost

16. Instrument Grade

Used for test ports

Economy calibration kits

Good performance

Tight tolerances

Dielectric supported interface

Long life

17. Production (Field) Grade

Systems and device connector

Low performance

Loose tolerances

Dielectric supported interface

Limited number of connections

Lowest Cost
Always Inspect Before Connecting

18. Connector Examples
Type F
BNC
SMC
Type N
APC 7
SMA
3.5 mm
2.92 mm or K
2.4 mm
MaleFemale FemaleMale

19. 3.5 mm Connectors

20. dmdDA
B
C
MP
OUTER CONDUCTOR
MATING PLANE
A D d
C
FP
OUTER CONDUCTOR
MATING PLANE
3.5mm Connector Detail

21. SMA Connectors

22. Coaxial Connectors – Operating Frequency

23. Connector Torque Limits

24. Connector Compatibility

3.5mm and 2.92mm connectors will mate, but have
mismatch

SMA will mate with 3.5mm and 2.92mm

Be careful with low quality SMA male connectors –
pin on high side of tolerance range can damage
precision 3.5 / 2.92 female

2.4mm and 1.85mm connectors will mate, but have
mismatch

25. Cleaning
 Apply a mild blast of dry compressed air or Nitrogen
 Use the minimum amount of pure alcohol
 Use lint-free cleaning tools (swab or brush)
 Do not use acetone, methanol, or CFCs (Freon).

26. Further Reading….
lResources:
lhttp://www.npl.co.uk/electromagnetic/
clubs/anamet/connector_guide.pdf

27. Agenda
 RF Connectors
 A significant factor in repeatability
and accuracy
 Selecting the best of several types
for application
 Compatibility
 Connectors are consumables
 limited lifetime
 damaged connectors are costly
 proper care maximizes lifetime
 VNA
 What is a Vector Network
Analyzer?
 How will a VNA help with Signal
Integrity?
 Calibrating and (De)Embedding
 What is TDR?
 The VNA approach to TDR

28. 28
Why use Vector Network Analysis?
 Very low level signals can be measured more accurately with
narrow bandwidths
 Can measure very fast Rise Times
 The 4-port, single-ended S parameters have become a de-facto
standard for describing the electrical properties of any 4-port
interconnect.
ı For example, IEEE P802.3ap Task Force uses measured S-parameters as test cases
[9] for proposed solutions to the problem of 10 Gbit/s Ethernet over backplanes.
 What are the numbers in S..
o the first index being the going out port
o the second index is the coming in port.
o Example: Gain or Loss of Device is S21

29. 29
What are we Actually Measuring?
 A network analyzer is an instrument that measures the
network parameters of electrical networks
 Network analyzers commonly measure s–parameters because
reflection and transmission of electrical networks are easy to
measure at high frequencies
 Measures Amplitude and Phase into and out of each DUT port

30. Typical Device Behaviour
Device
Incident
Reflected
Transmitted

31. Transmission Line Model

32. Signals are Complex Quantities
M
agnitude
Phase
Vector Ratios :
Vector Representation

33. Calibration and Reference Plane
 Defines Measurement Reference
 Linear Magnitude = 1.0 (0 dB)
 Phase = 0 Degrees
 (Reflection and Transmission)
 Establishes Characteristic Impedance, Z0
Port 1 Port 2
Port 1
Reference Plane
Port 2
Reference Plane

34. What is a Vector Network Analyzer?
 A Vector Network Analyzer (VNA) is an instrument that
measures the amplitude and phase of an electrical network
 A VNA typically displays S-parameter.
ZNB ZVA

35. What is a Vector Network Analyzer?
PROCESSOR / DISPLAY
INCIDENT
(R)
Incident
Reflected
Transmitted
a1
b1
a2
b2
Port 1 Port 2
SIGNAL
SEPARATION

36. What is a Vector Network Analyzer?
 Dual Directional Coupler
 Directivity is a measure of how well a coupler can separate
signals moving in opposite directions
Test port
(undesired leakage
signal)
(desired reflected
signal)
Directional Coupler
b a

37. What is a Vector Network Analyzer?
 Each port of a VNA contains a stimulus along with forward and
reverse measurement
 Typical Measurement example: Stimulate Port 1
PORT
Meas. Receiver “b”
Ref. Receiver “a”
Reflectometer
Incident
(“a1” receiver)
Reflected
(“b1” receiver)
Transmitted
(“b2” receiver)
Port 1 Port 2
DUT

38.  S-Parameters of a 2 port network
 S11 (b1/a1)
Forward reflection coefficient (input match, return loss, VSWR)
 S21 (b2/a1)
Forward transmission coefficient (gain or loss)
 S12 (b1/a2)
Reverse transmission coefficient (reverse isolation)
 S22 (b2/a2)
Reverse reflection coefficient (output match, return loss, VSWR)
Pin-refl
Pout
Pin
Prev-refl
Prev
What is a Vector Network Analyzer?

39. What is a Vector Network Analyzer?
Transmitted
Incident
TRANSMISSION
Gain / Loss
S-Parameters
S21, S12
Group
Delay
Transmission
Coefficient
Insertion
Phase
Reflected
Incident
REFLECTION
Standing Wave Ratio
SWR
S-Parameters
S11, S22
Reflection
Coefficient
Impedance,
Admittance
R+jX,
G+jB
Return
Loss
Γ, ρ
Τ,τ
Incident
(“a1” receiver)
Reflected
(“b1” receiver)
Transmitted
(“b2” receiver)
b1
a1
=
b2
a1
=
Port 1 Port 2
DUT

40. Measuring the Step Response
 In practice, it is easier to generate a step response as
compared to an impulse response
 Implementation of a TDR measuring device is shown
below:
 This device can measure the measure the Reflected Step and Impulse
responses, ГΘ(t)and Гh(t)respectively

41. Impulse and Step Response Examples
OPEN
SHORTImpulse
Step
Impulse
Step

42. The VNA approach to TDR
 The VNA measures in the Frequency domain
 In many instances, the process of converting to the Frequency
Domain, performing the analysis, and then converting back to
the Time Domain is easier.
 It is often times advantageous to measure in the Frequency
Domain instead of the Time Domain in order to get the Impulse
Response.
 Applying the Inverse Fourier Transform converts the frequency
response to the time domain.
 Advantages:
• Higher Dynamic Range: Lower instantaneous BW required, than a time
domain measurement
• Analog to Digital Converter in the Time Domain measurement limits the
frequency response.

43. Applications of TDR
 Examination of faults in transmission lines
 RF imaging for nondestructive evaluation
 Separation of echo from the wanted signal in case of
multipath propagation
 Moving the reference plane across unknown
irregularities

44. Measurements with VNAs on Cables
 Classical VNA measurements
 S-parameters
 Transmission, Reflection, cross coupling
 Fext, Next
 Group delay
 Electrical length
 TDR measurements
 Fault Location
 Rise Time
 Skew (interpair and intrapair)
 Impedance
 Quality of connectors

45. Relationship between Frequency Domain and
Time Domain
f 2f 3f 4f 5f 6f 7f freq
time
Inverse Fouriertransformation
Fouriertransformation

46. Examples for Rise Times and Resolution
ZNB 8: 60 ps
ZVA20: 25 ps
ZVA40: 13 ps

47. Time Domain Measurements
 Fault Location
 Skew
 Impedance vs Distance
 Gating
 Connector, Junction or Solder Charecteristics
 Resolution Enhancement

48. Time Domain Measurement Results
 Board: Micro stripe Line, Length of the Line: 49mm,
 Er ~ 3, SMA Connector and FarEnd SMA connector:
Open
 Low Pass Impulse Response:
1
1
2
3
4
Reflection SMA connector
2 Reflection SMA connector
To PCB
3 Reflection PCB to SMA
connector
4 Reflection SMA connector
(OPEN)

49. Time Domain and Frequency Domain
l Impedance l Insertion Loss
Cables can be verified by using the best suitable Domain
(time domain and/or frequency domain)

50. Measurement of a Connector with Time Domain
 Gating functionality can be used to suppress unwanted
reflections
 Gated time domain measurements can be re transformed
into frequency domain
 Typical application
o Test of the quality of a cable connector

51. Test of the Quality of a Connector
 Problem
o Test the quality of a connector soldered to a cable
o The other end of the cable has no connector at the other end to
solder it directly to a module
 Solution
o Isolate the connector by gating
o Measurement of the gated S11

52. 52
Time Gating
 Frequency Domain Analysis does not always provide
insightful analysis of devices with multiple reflections
-> Time Domain Reflectometry can provide this
 Example below of Time Domain vs. Frequency Domain
measurements: Which is easier to interpret??
OR

53. Time Gating (con’t)

54. Result
S11 with perfectly
matched Port 2

55. Reslution and Resolution Enhancement Factor
0,00E+00
5,00E-02
1,00E-01
1,50E-01
2,00E-01
2,50E-01
3,00E-01
3,50E-01
-2,00E-09 0,00E+00 2,00E-09 4,00E-09 6,00E-09 8,00E-09 1,00E-08 1,20E-08
time [ns]
ReflectionFactor[U]
ZVA: 1 GHz - 20 GHz ZNB: 1 GHz - 8 GHz REF: 2.5
ZVA: Start: 10 MHz - 20 GHz
ZNB: Start 10 MHz - 8 GHz, REF: 2.5
fstep: 10 MHz