12 VSWR Measurements

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Kathrein T. Wulff 07/2002

Field Measurements

Return Loss Measurements of

Kathrein Antennas

HP Network Analyzer(our reference, since commonly used at Kathrein-Werke KG)

versus

Portable Equipment

Equipment

Calibration

Accuracy

Common Problems

Charts

Antennas, narrowband sweep

Antennas, broadband sweep

Mismatch load, broadband sweep

Disclaimer

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Conclusion

Kathrein-Werke KGRosenheimPO Box 10 04 44

Phone:+ 49 (0)8031 184 - 0

Fax: +49 (0)8031 184 991

[email protected]


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Return Loss Measurements Site Installations

Field Installation is demanding on staff and equipment

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What needs to be done:

Mast needs to be installed

Cabling needs to be mounted

Antennas will be installed at the mast

Final Acceptance Test needs to be performed

Qualify successful installation ofall components

Measure electrical parameters ofindividual parts

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The Measurement Equipment



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Return Loss Measurements Equipment

Different measurement instruments are available at the

market to meet most customer requirements.

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Measurement equipment is exposed to a changing

environment once used in the field. High as well as

low ambient temperatures combined with high or low

humidity, dust, dirt, and improper handling are typical

with many installations.


What need to be considered?


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Portable Equipment is a very popular measurement tool

Convenient, and easy handling

Robust design

Intermediate up to high accuracy

Sometimes sensitive against high electromagnetic fields

HP 8753(XX) made by Hewlett Packard is also a very popularmeasurement tool commonly used for R&D purposes andacceptance tests on sites

Reliable instrument High accuracy

Difficult to handle on sites due to the high weight and large overalldimensions

e. g.

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Return Loss Measurements Calibration

HP Calibration

A variety of different calibration options is available

Re-calibration recommended whenever a new site will be measured

A jumper cable, if required, placed between DUT (Device Under Test, e.g.antenna) and Network Analyzer needs to be included in the calibrationprocess

An accidentally disconnected jumper cable will destroy calibration

immediately

Portable Equipment

Sometimes limited calibration options

Re-calibration recommended whenever a new site will be measured A jumper cable, if required, placed between DUT and Network Analyzer

needs to be included to the calibration process

Calibration sometimes relatively insensitive against accidentally

disconnected jumper cables 9/22Home


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Return Loss Measurements Accuracy

Portable Equipment/HP Accuracy

In general both, scalar and vector measurement systemssuffer with accuracy caused by hardware components used

inside the instruments.

Quality of the hardware components combined with internal

corrective operation procedures will determine final

accuracy of the displayed measurements.

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Portable Equipment/HP Accuracy

The calibration process finally determines the overall

performance of the system used for a certain qualificationprocess (e.g. antenna measurements). Calibration needs to

be performed carefully paying attention to proper calibration

standards (short, open, 50 Ohm load).

Moreover, its mandatory to enable

the correct connector types to matchRF connections of DUT.

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Return Loss Measurements Common Problems

Portable Equipment/HP

Quite often we experienced that

installation teams do not use

appropriated calibration standards,

or do not pay attention to

calibration requirements

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Return Loss Measurements Calibration Standard

HP Calibration / Portable Equipment Calibration

Instrument calibration is the most important step to probably

setup your equipment.

We strongly recommend to regularly measure and qualify

calibration components such as short, open, and50 Ohm termination.

Always use all three calibration components throughout the

entire calibration process.

Always handle calibration sets carefully.

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Portable Equipment /HP

We also experienced that jumper

cables quite often suffer with

adequate RF performance.

Kathrein-Werke KG uses special

measurement cables with

advanced return loss and

appropriated phase stability.

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Summary of common measurement problems

Additional adapters:

Adding adapters to match different RF connections will impact

measurement results

Additional cabling: Adding any further jumper cables will destroy accuracy of

measurement results due to phase errors and matching

errors

Strong RF fields of other base stations:

High electromagnetic fields from other sites may impact

sensitivity of measurement equipment

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Portable Equipment: Possible measurement errorsas stated in Reflectometer Measurements - Revisited, Application Note from a popular

measurement equipment manufacturer

DUT with VSWR of 1.222 (20 dB return loss) S11 maximum: (20 + 0.9151) dB = 20.915 dB (VSWR of 1.198)

S11 minimum: (20 - 0.8279) dB = 19.172 dB (VSWR of 1.247)

HP Network Analyzer: Possible measurement errorsas calculated with Agilents Uncertainty Calculator Program; referred to HP8753E; Full Two Port

Calibration; calibrated with 85032B calibration set

DUT with VSWR of 1.222 (20 dB return loss) S11 minimum: (20 + 0.52 ) dB = 20.52 dB (VSWR of 1.208)

S11 maximum: (20 - 0.49) dB = 19.51 dB (VSWR of 1.237)

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Return Loss Measurements

Portable Equipment versus HP

Comparison Measurements of Antennas

Examples

Narrow Band Sweep

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Return Loss Measurements Charts

HP Results Portable Results Delta Deviation

Marker 1: -15.653 dB -15.19 dB dB = 0.463

HP8753E Portable Equipment

Note: Different HP Network Analyzer or portable equipment might deliver test results that vary from the one displayed above.

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Comparison Measurements of Antennas

Examples

Broad Band Sweep

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Marker 1: -20.013 dB -20.26 dB dB = 0.247

Marker 2: -15.732 dB -15.24 dB dB = 0.492

HP8753E Portable Equipment


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Comparison Measurements of a

Mismatched Load

Examples

Broad Band Sweep

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-25,0

-22,5

-20,0-17,5

-15,0

-12,5

-10,0

-7,5

-5,0

-2,5

0,0

1000 1250 1500 1750 2000

M1 M2

Return Loss

Model: Serial #: 00000000Date: Time:Resolution: 130 CAL: ON(COAX)

dB

Frequency (800,0 - 2200,0 MHz)

M1: -15,29 dB @ 995,30 MHz M2: -2,21 dB @ 2004,70 MHz



Marker 1: -15.604 dB -15.29 dB dB = 0.314

Marker 2: -2.232 dB -2.21 dB dB = 0.022


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Conclusion

In essence not only the measurement

equipment, but basically the calibration processwith adequate standards, and jumper cables is

finally responsible for the overall measurement

accuracy.

Installation crews need to be aware about the

sensitivity, and about proper procedures toachieve best measurement results to avoid

unnecessary confusion about system

performance.HomeHome

12 VSWR Measurements

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