Impact of Mismatch Loss on Mobile Phone Simulation for Automotive - - PowerPoint PPT Presentation

Impact of Mismatch Loss on Mobile Phone Simulation for Automotive Testing

• R. Keith Frazier

Ford Motor Company

Introduction

Cellular Phones have become an integral part of automotive environment.

• Although the TX power is low, near field electric and

magnetic fields can be significant

Automotive International Standards

ISO 11451-3 and 11452-9 specify requirements & test methods for mobile RF devices inclusive of cellular phones.

– Mobile device is simulated with using a broadband RF source and antenna.

ISO 11452-9 Antenna and Setup

ISO 11452-9 Antenna and Setup

ISO 11452-9 Antenna Field Characteristics

F=400 MHz F=900 MHz F=1.8 GHz F=2.0 GHz F=2.45 GHz F=2.6 GHz

E FIELD @ 1W

ISO 11452-9 Antenna Field Characteristics

F=400 MHz F=900 MHz F=1.8 GHz F=2.0 GHz F=2.45 GHz F=2.6 GHz

H FIELD @ 1W

Antenna Positioning (50 mm spacing)

ISO Stress Levels

Stress levels are in terms of net power delivered to the

• antenna. The net power is expressed as:

RM FM NA

P A P A P ⋅ − ⋅ = 1

A

ISO Assumptions

• ISO standards assume the net power can be accurately

determined by:

1) The forward and reflected power measured at the coupler 2) The transmission loss of the interconnect between the antenna and directional coupler

• If this is true, the VSWR of the antenna can be accurately

determined by these 3 quantities

ISO Assumptions

A

ρ

FM RM C

P P = ρ

FM RM calc A

P P A 1

_

= ρ

Since: Therefore:

A C

A ρ ρ ⋅ =

Comparison of Calculated and Measured Antenna VSWR

( ) ( )

A A

VSWR ρ ρ − + = 1 1

( ) ( )

calc A calc A

VSWR

_ _

1 1 ρ ρ − + =

Net Power Error

• The relationship between the net power and forward

power to the antenna is:

• The resulting error in net power delivered to the antenna

is:

( )

2

1

A FA NA

P P ρ − ⋅ =

( ) ( ) 

       − − ⋅ =

2 2 _

1 1 10 ) (

A calc A

Log dB Error ρ ρ

Net Power Error

The Effect of Mismatch Error

S-parameters of single cable between the antenna and directional coupler.

2 22 1 21 2

a S a S b + =       ⋅       ⋅ ⋅ =      

2 1 22 21 12 11 2 1

a a S S S S b b

The incident signal at the antenna:

A

b a Γ =

2 2 A

S a S b Γ − =

22 1 21 2

1

therefore:

1 21 2

a S b ≈

but:

The Effect of Mismatch Error

S-parameters of single cable between the antenna and directional coupler.

      ⋅       ⋅ ⋅ =      

2 1 22 21 12 11 2 1

a a S S S S b b

The reflected signal seen at the directional coupler: Therefore:

2 12 1 11 1

a S a S b + =

Assuming small:

A

S Γ

22

[ ]

A

S S S a b Γ + =

21 12 11 1 1 A C

S S S a b Γ + = = Γ

12 21 11 1 1

The Effect of Mismatch Error

Considering Magnitude Only:

11 12 21

S S S

A C C

± = Γ = ρ ρ

A C

S S S a b Γ + = = Γ

12 21 11 1 1

Magnitude Only

The Effect of Mismatch Error

Impact of inclusion of a single adaptor between the antenna and directional coupler.

( ) [ ] ( ) [ ]

44 34 43 44 33 22 22 33 44 33 34 43 33 12 21 11

1 S S S S S S S S S S S S S S S S

A A C

− − Γ + − − Γ + + = Γ

The Effect of Mismatch Error

( ) [ ] ( ) [ ]

44 34 43 44 33 22 22 33 44 33 34 43 33 12 21 11

1 S S S S S S S S S S S S S S S S

A A C

− − Γ + − − Γ + + = Γ Assuming

33 11 12 21

S S S S

A C

+ + Γ = Γ

Therefore:

The Effect of Mismatch Error

( ) [ ] ( ) [ ]

44 34 43 44 33 22 22 33 44 33 34 43 33 12 21 11

1 S S S S S S S S S S S S S S S S

A A C

− − Γ + − − Γ + + = Γ Assuming

∑

=

± ≈

N i i A C

S S S

1 11 12 21

ρ ρ

Magnitude Only

33 11 12 21

S S S S

A C

+ + Γ = Γ

Therefore:

Interconnect Test Samples

Cable Only Cable + Adaptor

VNA

P1 P2

Sample Sample:

(1) 7M LMR-400 Ultraflex with Type N Connectors (2) Cable + Type N Bulkhead Adaptor

Mismatch Effect of Cable Only (C)

Cable VSWRMAX ~ 1.1

C A

Mismatch Effect of Cable + Adaptor

Cable/Adaptor VSWRMAX ~ 1.4

C A

Mismatch Impact on Net Power

∑

=

⋅ ± ≈

N i i A calc A

S A

1 11 _

1 ρ ρ

therefore:

FM FA

P A a S b P ⋅ = = =

2 1 2 21 2 2

PRM

∑

=

± ⋅ ≈

N i i A C

S A

1 11

ρ ρ A

C calc A

1

_

⋅ = ρ ρ but: ( Per ISO)

Mismatch Impact on Net Power

( ) ( ) 

       − − ⋅ =

2 2 _

1 1 10 ) (

A calc A

Log dB Error ρ ρ

Interconnect VSWR

7m LMR-400 Ultraflex with Type N Connectors

Uncertainty

Impact of Cable Transmission Loss

∑

=

⋅ ± ≈

N i i A calc A

S A

1 11 _

1 ρ ρ

LMR-400 Ultraflex (~ 0.25dB /m @ 2000 MHz)

( ) ( ) 

       − − ⋅ =

2 2 _

1 1 10 ) (

A calc A

Log dB Error ρ ρ

Cable VSWR < 1.1

Original Test Setup

DC1 DC2 S1 S2 Coaxial Switch Coaxial Switch

PS PS

Bulkhead Connector Chamber Wall Antenna

Improved Test Setup

Werlatone C7711

Insitu Measurements of VSWR and Transmission Loss

< 1.2 < 2.7

Performance Improvements

Interconnect VSWR limited < 1.2 Transmission loss limited to < 2.7 dB

Other Sources of Error

• Coupler VSWR
• Coupler Transmission Loss and Coupling Factor
• Coupler directivity
• Interconnect Transmission Loss Measurement Error

Other Sources of Error

Coupler Transmission VSWR, Transmission Loss and Coupling Factor

P1 P2 P3 P4

PS PF PFM ADC

Other Sources of Error

Coupler Directivity

Directivity of AR DC7144A

Other Sources of Error

Coupler Directivity

Directivity of AR DC7144A

< -18dB

Other Sources of Error

Interconnect Transmission Line Error

Recommend < 0.1 dB ripple

Summary

• Mismatch losses can significantly impact uncertainty in

net power delivered to the transmit antenna if not limited.

– Transmission loss of the interconnect also contributes

• Recommend limiting mismatch and transmission loss of

interconnection.

– Net power error < ± 1db if VSWR< 1.3 and A < 4 db.

• Recommend insitu characterization of test setup’s

complete interconnection between the antenna and directional coupler.

Summary

Recommended Coupler Requirements

– Coupling Factor: > 20 dB (40 dB preferred)

• Selection must be compatible with sensitivity of power sensor

– Transmission Loss: < 0.5 dB – VSWR: < 1.3:1 – Directivity (magnitude): > 18 dB

Summary

Limiting mismatch facilitates use of forward power only to characterize the test setup. ( )

2 22 2 2

1

A FM FA

S A P b P ρ ± ⋅ = =

A

S a S b Γ − =

22 1 21 2

1

( )

( ) 

       − ⋅ ± ⋅ =

2 2 22

1 1

A A NA FM

A S P P ρ ρ

( )

2

1

A FA NA

P P ρ − ⋅ = therefore: but:

Summary

Limiting mismatch facilitates use of forward power only to characterize the test setup. ( )

( ) 

       − ⋅ ± ⋅ =

2 2 22

1 1

A A NA FM

A S P P ρ ρ therefore: if mismatch small 1

22

<<

A

S ρ

( )

2

1

A NA FM

A P P ρ − ⋅ =

Summary

Limiting mismatch facilitates use of forward power only to characterize the test setup. ( )

( ) 

       − ⋅ ± ⋅ =

2 2 22

1 1

A A NA FM

A S P P ρ ρ therefore: if mismatch small 1

22

<<

A

S ρ

( )

2

1

A NA FM

A P P ρ − ⋅ =

Monitoring the reflected power still recommended to verify stability of test setup

PRM

Summary

Impact on Laboratory

– Invest in a Vector Network Analyzer – Dedicated test setup or extensive re-characterization prior to every test. – Consideration should be given toward a dedicated portable setup.

• Used within test chamber.
• Keeps signal source, cabling and antenna together
• Does require power within the test chamber

References

1) ISO 11451-3: Road vehicles- Vehicle test methods for electrical disturbances from narrowband radiated electromagnetic energy – Part 3: On-board transmitter simulation. 2) ISO 11342-9: Road vehicles – Component test methods for electrical disturbances from narrowband radiated energy – Part 9: Portable transmitters. 3) M. Dobbert, “Revisting Mismatch Uncertainty with the Rayleigh Distribution,” NCSL International Workshop and Symposium 2011, pp. 8-9.

Thank You