high power measurements using the agilent nonlinear vector

May 26, 2010

presented by:

Keith Anderson

Senior R&D Engineer/Scientist

Agilent Technologies

© Copyright 2010 Agilent Technologies, Inc.

High Power Measurements

using the

Agilent Nonlinear Vector Network Analyzer

April 2010

Agenda

•Test Devices (problem)

•Nonlinear Measurements (solution)

•High-Power Modifications

•Example Setup

•Summary and Conclusion

April 2010

High-Power Devices

•What qualifies as "high-power"?

• 1W to 1kW

• Operating at RF frequencies

•What is being measured?

• Transistors

• Amplifiers

• Subsystems (e.g. TR Modules)

April 2010

Applications

• Mobile phones

• Base stations

• Satellite systems

• Radar

http://www.mrao.cam.ac.uk/research/alma.jpg

April 2010

Nonlinearity

•Most high-power amplifiers are nonlinear

• Operate near compression to maximize power

• Measure near compression to properly characterize

• Nonlinear measurements include

• Gain Compression

• Distortion

• Load pull

April 2010

Problems

• Complete characterization of amp requires many

measurements

• Modeling nonlinear devices with linear measurements

results in incomplete characterization

• Circuit simulations of nonlinear devices are inaccurate

• Test equipment has power limitations

April 2010

Agenda




•Example Setup


April 2010

Measurement Solution

•Measure amplifier with Agilent Nonlinear Vector Network

Analyzer (NVNA)

•Modify NVNA to handle high power levels

•Measure X-parameters* of amplifier

•Use X-parameters for nonlinear circuit simulation

* "X-parameters" is a registered trademark of Agilent Technologies. The X-parameter format and underlying equations are open

and documented. For more information visit http://www.agilent.com/find/eesof-x-parameters-info

http://www.agilent.com/find/eesof-x-parameters-info







April 2010

NVNA Overview

•Stimulate amplifier input with Main Tone

•Stimulate amplifier input and output with Extraction Tone

•Vary frequency and power of tones

•Measure all waves

•Extract X-parameters

R1 A

R3 C

NVNA

Main Tone

Extraction Tone

Amp

Port 1

Port 3

Combiner ReferenceCoupler

TestCoupler

TestCoupler

ReferenceCoupler

TransferSwitch

Agenda




•Example Setup


April 2010

Amplifier Considerations

•P1dB, Psat, Gain

•Match requirements

•Power supply sequencing

•Amp settling (heating effects)

April 2010

AmpP1dB & Psat

V1 V2

Gain

Load

MatchSource

Match

Power

NVNA Considerations

•RF & DC damage levels

•Output power

•RF path losses

•Receivers (R1, A, R3, C)

• Distortion level

• Noise floor

• Direct receiver access

April 2010

R1 A

R3 C

NVNA

Main Tone

Extraction Tone

Amp

Port 1

Port 3


TestCoupler

TestCoupler

ReferenceCoupler

TransferSwitch

NVNA Block Diagram

April 2010

Adding Attenuator (1)

Attenuator at test port

•Improves match

•Protects components

•Degrades measurement stability

•Recommend: <10dB attenuation

•Recommend: Attenuator close to coupler

April 2010

R3

Port 3

C

Amp

Extraction

tone

Reference

coupler

Test

coupler


Attenuator between couplers

•Improves match

•Protects components

•Recommend: Short cables

April 2010

R3 C

AmpPort 3

Extraction

tone

Reference

coupler

Test

coupler


April 2010

Attenuator at receiver

•Protects receivers

•Improves distortion

•Recommend: Receiver power < -20dBm

•Recommend: Short cables

R3 C

AmpPort 3

Extraction

tone

Reference

coupler

Test

coupler

Adding Pre-amplifier (1)

April 2010

Driving test amplifier input

•Provides power to drive test amplifier into compression

•Recommend: Pre-amp distortion < -20dBc

R1Pre-amp

A

AmpPort 1

Extraction

tone

Reference

coupler

Test

coupler

Main

tone

Adding Pre-amplifier (2)

April 2010

Driving test amplifier output

•Pre-amp drives "extraction tone" into test amplifier output

•Recommend: Extraction tones between -20dBc and -40dBc

•Note 1: Test amplifier drives large signal into pre-amp output

•Note 2: Pre-amp distortion is not a problem

R3Pre-amp

C

AmpPort 3

Extraction

tone

Reference

coupler

Test

coupler

Adding Coupler

April 2010

•Replace internal coupler with high-power coupler

•Requires direct receiver access

•Will typically also add attenuators or pre-amps

•May change frequency response

•Recommend: Short Cables

R3 C

(unused)

Port 3

Amp

Reference Coupler

TestCoupler

Extraction

tone

R3C

(unused)

Port 3

Amp

TestCoupler

Reference Coupler(unused)

Extraction

tone

R3 C

(unused)

Port 3

Amp

TestCoupler

Reference Coupler

Extraction

tone

Agenda




•Example Setup


April 2010

Goals

April 2010

•Measure 63W amplifier

• Frequency = 100M-500MHz

• Gain = +14dB

• P1dB = +48dBm

•Modify NVNA

• Provide high power to test

amplifier

• Protect NVNA from damage

• Avoid receiver distortion

• Avoid noise

R1 A

R3 C

NVNA

Main Tone

Extraction Tone

Amp

Port 1

Port 3


TestCoupler

TestCoupler

ReferenceCoupler

TransferSwitch

Block Diagram Modifications

April 2010

Port 1

A Freq = 100M-500MHzP1dB = +48dBmGain = +14dB

Amp

R1

40dB40dB

Port 3

R3 C

10dB4dB

43dB40dB

Extractiontone

Maintone

NVNA

TestCoupler


Reference Coupler

TestCoupler


Reference Coupler

Input side: Pre-amp

•Pre-amp drives test amplifier input at +34dBm

•Pre-amp Pout = +35dBm

•Pre-amp may operate into open or short-circuit

•Recommend: Ensure distortion < -20dBc

April 2010

Amp

P1dB = +48dBmGain = +14dB

Port 1

AR1

40dB40dB

+35dBm +34dBm +48dBmMaintone

Extractiontone

Input side: Coupler

•Replace internal reference coupler

• NVNA reference coupler damage level = +30dBm

• External reference coupler Pmax > 41dBm

•Note: NVNA test coupler damage level = +43dBm

April 2010

Amp


Port 1

AR1

40dB40dB


Extractiontone

Testcoupler

Referencecoupler

(unused)

Input side: Attenuators

•Receiver attenuators limit power level to -20dBm

•Minimizes distortion and protects receivers

April 2010

Amp


Port 1

AR1

40dB40dB


Extractiontone

Output side: Pre-amp

•Provides +18dBm (= +48dBm - 30dBc) extraction tone

•Pre-amp Pout = +33dBm

•Reverse power may equal forward power

•Pre-amp may operate into open or short circuit

April 2010

+48dBm+18dBm

Port 3

R3 C

10dB

43dB40dB

+33dBm+33dBm

Amp

Extractiontone

4dB

Output side: Coupler

•Replace internal reference coupler

• NVNA reference coupler damage level = +30dBm

• External reference coupler Pmax > 39dBm

•Note: NVNA test coupler damage level = +43dBm

April 2010

+48dBm+18dBm

Port 3

R3 C

10dB

43dB40dB

+33dBm+33dBm

Amp

Extractiontone

4dB

Testcoupler

Referencecoupler

(unused)

Output side: Attenuators

• 10dB attenuator limits test coupler power to +40dBm

• Attenuators and couplers limit power incident on the pre-amp

to +33dBm

• Receiver attenuators limit receiver power to -20dBm to

minimize distortion and protect receivers

April 2010

+48dBm+18dBm

Port 3

R3 C

10dB43dB40dB

+33dBm+33dBm

Amp

Extractiontone 4dB Test

coupler

Agenda




•Example Setup


April 2010

High-power Considerations

•Beware of RF and DC maximum levels

•Add voltages when calculating maximum signal levels

•Consider match requirements of test amplifier and pre-amps

•Consider power-on sequencing of test amplifier and pre-amps

•Use short, semi-rigid RF cables to optimize stability

•For NVNA, set "power limits" and define "user preset" to avoid

accidentally damaging test amplifier or system components

April 2010

Conclusion

•High-power amplifiers require nonlinear characterization

•Nonlinear Vector Network Analyzer (NVNA) characterizes

nonlinear devices by measuring X-Parameters

•NVNA is easily modified to test high-power devices

April 2010

Information Sources

Agilent's high-power NVNA application note

www.agilent.com/find/pnaxapps

Agilent’s Nonlinear Vector Network Analyzer

www.agilent.com/find/nvna

Agilent’s PNA-X network analyzers

www.agilent.com/find/pnax

April 2010

http://www.agilent.com/find/pnaxapps

http://www.agilent.com/find/nvna



Are there any Questions?

April 2010

high power measurements using the agilent nonlinear vector

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