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 E FIELD @ 1W F=400 MHz F=900 MHz F=1.8 GHz F=2.0 GHz F=2.45 GHz F=2.6 GHz

ISO 11452-9 Antenna Field Characteristics H FIELD @ 1W F=400 MHz F=900 MHz F=1.8 GHz F=2.0 GHz F=2.45 GHz F=2.6 GHz

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: 1 P = A ⋅ P − ⋅ P NA FM RM A 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 ρ = A ρ ⋅ ρ C A A P RM ρ = Since: C P FM 1 P Therefore : RM ρ = A _ calc A P FM

Comparison of Calculated and Measured Antenna VSWR ( ) 1 + ρ A _ calc VSWR = ( ) 1 − ρ A _ calc ( ) 1 + ρ A VSWR = 1 ( ) − ρ A

Net Power Error • The relationship between the net power and forward power to the antenna is: ( ) 2 P = P ⋅ 1 − ρ NA FA A • The resulting error in net power delivered to the antenna is:  ( )  2 1 − ρ A _ calc   Error ( dB ) = 10 ⋅ Log ( )  2  1 − ρ   A

Net Power Error

The Effect of Mismatch Error S-parameters of single cable between the antenna and directional coupler. The incident signal at the antenna: b = S a + S a 2 21 1 22 2 but: a = b Γ 2 2 A therefore: S a 21 1 b = 2 1 − S Γ 22 A       b S ⋅ S a 1 11 12 1       = ⋅ b ≈ S a       b S ⋅ S a 2 21 1 2 21 22 2

The Effect of Mismatch Error S-parameters of single cable between the antenna and directional coupler. The reflected signal seen at the directional coupler: b = S a + S a 1 11 1 12 2 Assuming small: S Γ 22 A [ ] b = a S + S S Γ 1 1 11 12 21 A Therefore: b       b S ⋅ S a 1 Γ = = S + S S Γ 1 11 12 1       = ⋅ C A 11 21 12 a       b S ⋅ S a 1 2 21 22 2

The Effect of Mismatch Error Considering Magnitude Only: b 1 Γ = = S + S S Γ C A 11 21 12 a 1 S S S ρ = Γ = ρ ± C C 21 12 A 11 Magnitude Only

The Effect of Mismatch Error Impact of inclusion of a single adaptor between the antenna and directional coupler. [ ( ) ] S S S + Γ S S − S S 21 12 33 A 43 34 33 44 Γ = S + [ ] C 11 ( ) 1 − S S + Γ S S S − S S − S 33 22 A 22 33 44 43 34 44

The Effect of Mismatch Error [ ( ) ] S S S + Γ S S − S S 21 12 33 A 43 34 33 44 Γ = S + C 11 [ ( ) ] 1 − S S + Γ S S S − S S − S 33 22 A 22 33 44 43 34 44 Assuming Therefore: Γ = S S Γ + S + S C 21 12 A 11 33

The Effect of Mismatch Error [ ( ) ] S S S + Γ S S − S S 21 12 33 A 43 34 33 44 Γ = S + C 11 [ ( ) ] 1 − S S + Γ S S S − S S − S 33 22 A 22 33 44 43 34 44 Assuming Therefore: N ∑ Γ = S S Γ + S + S ρ ≈ S S ρ ± S C 21 12 A 11 33 C 21 12 A 11 i i = 1 Magnitude Only

Interconnect Test Samples VNA P1 P2 Cable + Adaptor Sample Sample : Cable Only (1) 7M LMR-400 Ultraflex with Type N Connectors (2) Cable + Type N Bulkhead Adaptor

Mismatch Effect of Cable Only ( � C ) � C � A Cable VSWR MAX ~ 1.1

Mismatch Effect of Cable + Adaptor � A � C Cable/Adaptor VSWR MAX ~ 1.4

Mismatch Impact on Net Power P RM 2 2 2 P = b = S a = A ⋅ P FA 2 21 1 FM N 1 ∑ ρ = ρ ⋅ ρ ≈ A ⋅ ρ ± S but: ( Per ISO) A calc C _ C A 11 i A i = 1 N 1 ∑ ρ ≈ ρ ± ⋅ S therefore: A _ calc A 11 i A i = 1

Mismatch Impact on Net Power ( )   2 1 − ρ A _ calc   Error ( dB ) = 10 ⋅ Log ( )   2 1 − ρ   A Interconnect VSWR Uncertainty 7m LMR-400 Ultraflex with Type N Connectors

Impact of Cable Transmission Loss ( )   2 N 1 ∑ 1 − ρ A _ calc   ρ ≈ ρ ± ⋅ S Error ( dB ) = 10 ⋅ Log ( )  A _ calc A 11 i 2 A  1 − ρ   i = 1 A LMR-400 Ultraflex (~ 0.25dB /m @ 2000 MHz) Cable VSWR < 1.1

Original Test Setup Bulkhead Connector Antenna DC1 S1 Coaxial Switch DC2 S2 Chamber Wall Coaxial Switch PS PS

Improved Test Setup Werlatone C7711

Insitu Measurements of VSWR and Transmission Loss < 2.7 < 1.2

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 A DC P S P F P3 P4 P FM

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. S a 21 1 b = 2 1 − S Γ 22 A A 2 P = b = P ⋅ FA 2 FM ( ) 2 1 ± S ρ 22 A ( ) 2 but: P = P ⋅ 1 − ρ NA FA A therefore:   ( ) 2 1 ± S ρ   22 A P = P ⋅ ( )  FM NA 2  A ⋅ − ρ 1   A

Summary Limiting mismatch facilitates use of forward power only to characterize the test setup.   ( ) 2 1 ± S ρ   22 A P = P ⋅ ( )  FM NA 2  A ⋅ − ρ 1   A if mismatch small S ρ << 1 22 A therefore: P NA P = ( ) FM 2 A ⋅ 1 − ρ A

Summary Limiting mismatch facilitates use of forward power only to characterize the test setup.   ( ) 2 1 ± S ρ   22 A P = P ⋅ ( )  FM NA 2  A ⋅ − ρ 1   A if mismatch small S ρ << 1 22 A P RM therefore: P NA P = ( ) FM 2 A ⋅ 1 − ρ Monitoring the reflected power still A recommended to verify stability of test setup

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.

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