EuMW 2011 Agilent Workshop Series - keysight.com€¦ · Alignment: Frequent Self Adjustment – Automatic adjustment compensates for temperature, drift, aging – Alignment can affect

Copyright © 2011 Agilent TechnologiesCopyright © 2011 Agilent Technologies Inc.

Optimizing Performance and Best

Practices for Millimeter Measurements

Ben Zarlingo, Agilent Technologies

EuMW 2011 Agilent Workshop Series

Copyright © 2011 Agilent Technologies

© Agilent Technologies 2011

Agenda

Millimeter Measurements Discussion

– Information

– Best Practices

– Optimizing Performance

Special Hazards, Problems

References, Resources



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What is Millimeter-Wave?

Wavelengths ~≤ 10 mm, f ~≥ 30 GHz

Where Everything Gets

– Difficult

– Small

– Expensive

– Lossy

– Delicate

– Inflexible

– Banded (if not narrowband)

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Millimeter Performance Expectations

Performance Generally Less Ideal

– Harmonic architecture (phase noise, conversion loss, etc.)

– Path/insertion losses, impedance mismatches

– Preselector filtering



Importance of Cables, Connectors

Influence of Materials, Structures, Geometries

Amplitude, 30-50 GHz

– Dropouts due to moding*– Amplitude, phase errors

– Errors with 3.5mm also, though perhaps more repeatable

– Error < 2dB in this example• Good enough?

• Repeatable enough?

Performance Gain fromcables may be Less Expensive

2.4 mm

SMA

*Moding: Excitation of the first circular waveguide propagation mode in the coaxial structure



Plastic vs. Air Dielectric

Plastic (PTFE) vs. Air, Beads

– Air for metrology grade & many instrumentation grade

Many Other Tolerances & Construction Differences UsuallyAccompany Dielectric Change

SMA

3.5 mm



Use A Torque Wrench for Consistency

“Wrench Lift Stress” is a special concern with severaldevices connected or a long device or adapter(s)

Lift

Angle between wrenches should be less than 90 deg



Torque Values & Wrench Sizes



Torque Problem Example

Loose Cable AmplitudeError

– Significant for you?What if it is variable andinconsistent?

Phase Variability

Sufficient Torque

– Enough torque to properly matesurfaces and to produce a strainthat will prevent loosening dueto vibration and/or thermalcycling

– Not enough to damage or distortconnectors, changing geometry



Connector Grades

Metrology Grade– Highest precision, performance, repeatability

– Often slotless female center conductors (repeatable, lower inductance)

– Often used in calibration/verification kits

– Expensive, long life

PSC = Precision Slotless Connector – Typically metrology grade; PSC versions available for 3.5mm, 2.4 mm

Instrument Grade– Excellent repeatability, long life

– Often slotted female center conductors

General Purpose or Production Grade– Typical on components, cables, microstrip

– Inspect before connecting to better grades (analyzers), use adapter

– Limited connection cycles



Connection Consistency

Consistent Connections Improve Repeatability– Same Cables (cable loss may be more than 3 dB/meter at 50 GHz)

– Same connectors, adapters

– Same cable routing

Every Connection & Transition is Imperfect– Insertion loss (one adapter = up to 1 dB loss at 50 GHz)

– Impedance change

– Bending can change cable characteristics

– Consider semi-rigid cable

Analyzer Accuracy is Improving →→→→ Smaller Errors Matter

Repeatability may be More Important than Absolute Accuracy

Standardize on Highest Frequency Connectors?– Consistency, but slightly higher loss at lower frequencies



mm-Frequency Connectors and Intermating

24 pt level 1

– 20 pt level 2

• 18 pt level 3

http://na.tm.agilent.com/pna/connectorcare/What_mates_with_what.htm

Uses a plastic (PTFE) dielectric



NMD Connectors

Precision, Ruggedized

Provides Support

Stabilizes Connection

– The NMD connector is a ruggedized test-port connector used on Agilent test sets and network analyzers. Most often, the connectors used are 3.5mm and 2.4mm male connectors. These connectors include a large threaded body that is specially designed to stabilize the test port cable when attached to the front of the analyzer or test set using Agilent test port cables. The design of these connectors allows the use of standard female 3.5mm and 2.4mm cables and adapters.



Torque for Intermating

Proper Torque for Intermating Can Depend on Gender

– Example 1: A 56 N-cm. torque wrench should be used to connect male SMA connectors to either 3.5-mm or 2.92-mm (K) connectors

– Example 2: A 90 N-cm torque wrench should be used to connect male 3.5-mm or male 2.92-mm connectors to mating female connectors including SMA

Precision Connectors use Higher Torque

– Use lower torque with SMA ↔↔↔↔ SMA

– Use lower torque with male SMA male ↔↔↔↔ precision

Do not connect an SMA to a 3.5 mm calibration standard, VNA port cable or precision 3.5 mm device



Important Lower Frequency Connectionsin a High Frequency System

Connectors Make a Difference in Some Low Frequency Measurements!

3.5 mm or SMA to BNC

Precision BNC connections on Oscilloscope



Precision BNC - 3.5 mm vs. BNC - SMA

Air dielectric vs. PTFE

Split or slotted or hybrid center and outer connectors



Understand Your Measurement Plane

Goal is Consistent Measurement Plane

Make Connector/Adapter/Cable Choices to Reduce or Eliminate Removable Connection as Part of DUT

Consistent Torque, Cable Routing

Goal is Simplest, Shortest Path

More Critical for Network Analysis



Connection Corrections-Amplitude:Cables, Adapters, Probes



Phase-Matched ConnectionsDoes Phase Matter?

Spectrum, Power, Demodulation

– Spectrum, Power (channel/band, ACP, etc.) insensitive to phase

– Demodulation is insensitive, or corrects for phase for single channel

– Demodulation can be sensitive to phase for 2-channel (i+jQ) measurements (quadrature error varying with frequency)

– Flatter (over the measured span) is better for demod

– Wider spans/bandwidths are more demanding

Phase Stability

– Cable, connector movement a problem for close-in phase noise

– See also microphonics

Phase Repeatability

– Not a problem for most measurements



Coax & Waveguide Comparison

Flexible

Wide frequency range

Easy to change routing

Light weight

Can carry DC bias

Can be less expensive

Good match for component meas.

Disadvantages– Lossy, increasing with frequency

– Can be delicate

– Limited power handling

Low loss

High power handling ability

Mechanically durable

Disadvantages– Inflexible

– May need custom construction (expensive)

– Time delays for construction and reconfiguration

– Frequency range ≤ 1 octave

– Transitions needed to connect to analyzers, other coaxial elements

Coax Waveguide



Agenda

Millimeter Measurements Discussion

– Information

– Best Practices

– Optimizing Performance

Special Hazards, Problems

References, Resources



Beware of DC at Analyzer Input

Millimeter Agilent PXA, PSA Have No DC Block

Why? Internal DC Block Would Compromise Performance

Add External DC Block if Needed

Front Panel Male ConnectorProtects Analyzer

– Discourages direct mating withtypical coaxial male connector

– Encourages use of connector saver

– Male connector more durable,less likely to be damaged fromimproper mating



Adapters as Connector Savers

Connectors are “Consumables” with a Limited Lifetime

Non-Millimeter Instruments Typically use Female Front Panel Connector– Use to mate male cables with

male analyzer connector

– Consider other types as neededin your application

Note “Flats” for Wrenches to Prevent Connector Rotation



Contact Integrity, Concentricity

Visual Inspection, Suggest 10x Magnification

– Bending/displacement

– Non-concentric male or female

– Inspect mating planes for deep scratches, dents, debris

Damage to Female Slotted Connectors Most Common



Damage Hazard: Non-Captive SMA Nut

Danger from SMA Male to 2.4 mm and 1.85 mm Female

3.5 mm to 2.4 mm adapter

3.5 mm end 2.4 mm end

SMA with non-captive nutand extended center pin

SMA with non-captive nut can be inserted into 2.4 mm



Electrical Damage

High Frequencies →→→→ Small Size →→→→ Electrically Delicate

Burnout from Excess Power

Burnout from Source Transient

Static Zap

Detecting Damage (other than outright failure)



ESD Precautions

Wrist Strap

Table Mat

Heel Strap



Microphonics, Other Movement

Phase Noise, Close-In Modulation

Can Affect Analyzer, Connections, DUT

Mitigating Microphonics

– Separate table, mounting

– Use isolating feed/pads/mounts

– Stabilize or support cables, waveguide

– Use phase-stable cables

Vibration, Thermal Cycling may Loosen Connections

– Torque check as part of measurement routine



Alignment, Calibration, Correction

Calibration: Initial & Periodic Adjustment, Verification– Factory, service center, calibration lab

Alignment: Frequent Self Adjustment– Automatic adjustment compensates for temperature, drift, aging

– Alignment can affect dynamic range

Correction/Compensation– Often included in demodulation operations

– Substitution (power meters, etc.)

– May be only practical way to dramatically improve accuracy

– Enter parameters in analyzer for front-panel operation

– May be manually cumbersome or need switching

Perform Alignments Frequently and Whenever Measurement conditions Change– Temperature sensitivity generally goes up with frequency



Preselector Centering

YTF Preselector (Filter)

– YTF operates open-loop

– Preselector tuning is characterized automatically by analyzer for full frequency range

– Centering performed by analyzer, very brief operation

– Perform centering for best amplitude accuracy at a single frequency

– Centering is initiated by user; not part of normal alignment



Preselector Bypass

“Microwave Preselector Bypass”

Typically a Hardware Option

Removes YIG-Tuned Preselector Filter from Measurement Path

– Essential for wide-bandwidth measurements

– Removes preselector insertion loss but passeswideband noise; effect on analyzer DANLis variable

– May allow other signals into measurement

– Can tune to signal with preselector in placeand then bypass

Preselector

Bypass Path

Norm

Bypass



Vector Calibrations for Modulated, Wideband Signal Generation & Meas.

Scalar Amplitude Corrections

– Scalar measurements: amplitude, power, phase noise, noise figure

– Narrowband

– CW, narrowband signals

Vector (Complex) Corrections

– I/Q or amplitude/phase

– Modulated signals

– Wideband measurements

32



Example: RADAR Signal with IQ Errors

2 GHz Chirp: Gated sweep shows chirp spectrum and unwanted image from modulator IQ errors

33



RADAR Signal with IQ Corrections

800 MHz Chirp, 900 MHz Span: IQ-Correcting Modulated Signal Removes Almost All Image Energy

34



Combining Preamp and Attenuation

Preamp Improves Sensitivity

Attenuation Improves Match (reduces mismatch error)

Combine to Optimize Match & Sensitivity

35

Std PathLNP

Preamp



Hardware Features & Signal Processing Improve Performance

Low NoisePath

Noise FloorExtension

36

• Standard

• With LNP

• With NFE



New Calc. Method for Mismatch Uncertainty

Mismatch Uncertainty typically dominates

Better understanding, verification of probability distributions

Rayleigh model is an excellent fit, provides more accurate but still conservative estimates of uncertainty due to mismatch

Result: Lower Uncertainties due to mismatchby factor of 3 to 6

AN 1449-3 Power Measurement Uncertainty Per International Guidelines (updated April 2011)



Better Calculations Indicate a Rayleigh Distribution

Probability density of the magnitude of the reflection coefficient is Rayleigh distributed if the probability density of both complex parts is Gaussian distributed



Validating Assumptions with Real World Examples

Power

Sensor

Signal

Generator



Validating Assumptions with Real World Examples

Signal Analyzer



Additional InformationMicrowave and Millimeter Signal Measurements: Tools and Best Practices http://cp.literature.agilent.com/litweb/pdf/5990-8892EN.pdfFundamentals of RF and Microwave Power Measurements (part 3)Power Measurement Uncertainty Per International Guidelines AN-1449-3, April 2011 http://cp.literature.agilent.com/litweb/pdf/5988-9215EN.pdfAverage Power Sensor Uncertainty Calculatorhttp://www.home.agilent.com/upload/cmc_upload/All/Average_Power_Sensor_Uncertainty_calculator_Rev6.xlsx

Coaxial Connector Overviewwww.home.agilent.com/upload/cmc_upload/All/CoaxialConnectorOverview.pdf

What Mates With Whathttp://na.tm.agilent.com/pna/connectorcare/What_mates_with_what.htm

Connector Gradeshttp://na.tm.agilent.com/pna/connectorcare/Connector_Grades.htm

INTERMATEABILITY OF SMA, 3.5 MM AND 2.92 MM CONNECTORSMicrowave Journal (Cables & Connectors Supplement) 3/2007, available at www.gore.com

Connector Care Quick Reference Cardhttp://cp.literature.agilent.com/litweb/pdf/08510-90360.pdf

Principles of Connector Carehttp://cp.literature.agilent.com/litweb/pdf/5954-1566.pdf

External Waveguide Mixing and Millimeter Wave Measurements with Agilent PSA Spectrum Analyzers (app-note 1485)http://cp.literature.agilent.com/litweb/pdf/5988-9414EN.pdf

Documents

EuMW 2011 Agilent Workshop Series - keysight.com€¦ · Alignment: Frequent Self Adjustment – Automatic adjustment compensates for temperature, drift, aging – Alignment can affect