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June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 1
RF AntennaRF Antenna(RT-RFA)(RT-RFA)
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 2
RT-RFART-RFA
© Copyright 2001 Global Wireless Education Consortium
All rights reserved. This module, comprising presentation slides with notes, exercises, projects and Instructor Guide, may not be duplicated in any way without the express written permission of the Global Wireless Education Consortium. The information contained herein is for the personal use of the reader and may not be incorporated in any commercial training materials or for-profit education programs, books, databases, or any kind of software without the written permission of the Global Wireless Education Consortium. Making copies of this module, or any portion, for any purpose other than your own, is a violation of United States copyright laws.
Trademarked names appear throughout this module. All trademarked names have been used with the permission of their owners.
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 3
RT-RFART-RFA
Partial support for this curriculum material was provided by the National Science Foundation's Course, Curriculum, and Laboratory Improvement Program under grant DUE-9972380 and Advanced Technological Education Program under grant DUE‑9950039.
GWEC EDUCATION PARTNERS: This material is subject to the legal License Agreement signed by your institution. Please refer to this License Agreement for restrictions of use.
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 4
Table of ContentsTable of Contents
Overview 5
Learning Objectives 6
Antennas as Part of All Communications Systems 7
Fundamental Antenna Characteristics 12
Antenna Radiation Patterns 19
Antenna Types 27
Antenna Configuration Requirements 49
Signal Coverage Problems 56
Advanced System Antennas 63
Antenna Covers and Support Structures 71
Contributors 76
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OverviewOverview
How antennas transmit and receive signals
Fundamental characteristics of antennas
Types and features of antennas
Signal coverage problems and how to overcome them
How to perform return loss measurement and antenna gain measurement
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Learning ObjectivesLearning Objectives
Explain how an antenna transmits and receives signals Explain fundamental characteristics of antennas
including radiated power, antenna gain, beam width, and front-back ratio
Describe features of different types of antennas Describe the different types of radiation patterns
Explain why and how to measure impedance Explain strategies to address signal coverage problems
Explain antenna diversity and isolation strategies Perform a return loss measurement on an antenna Perform an antenna gain measurement
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Antennas as Part of All Antennas as Part of All Communications SystemsCommunications Systems
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Antenna System Antenna System ComponentsComponents
Transmit antenna Receive antenna Duplexer Multicoupler Combiner Isolator Tuning cavities Cabling
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Antenna OperationAntenna Operation
Antenna - a series of metal wires, rods, or other shapes Transmits when an electric current of radio frequency passes
through it
Current generates electromagnetic field around antenna
Electromagnetic field moves outward from antenna At receiver antenna, does same thing in reverse Tuned to a particular radio wavelength (λ)
Simple fraction or multiple of that length: λ/2, λ/4, etc. Most common length is one-half a wavelength, or λ/2
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Antennas, Frequency, and Antennas, Frequency, and WavelengthWavelength
Resonant length changes with frequency and wavelength of electric signal The higher the frequency, the shorter the wavelength, and the
shorter the required antenna The lower the frequency, the longer the wavelength, and the
longer the required antenna
Cellular band antenna Wavelength for cellular telephone transmission is about 0.33 m Length of a cellular antenna should be 0.165 m (λ/2)
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Assorted FactsAssorted Facts
Antenna Radiation Pattern Same radiation pattern and gain for transmit and receive antenna
Transceiver Transmitter and receiver electronics housed in a single box Generally use a single antenna for both
Impedance Match Coaxial cable must be terminated with characteristic impedance for
maximum power to be passed to antenna If not, reflections will reduce power passed to antenna and cause
protection circuitry in transmitter to reduce its output power
RF Transmission Planning Optimizes signal strength received by base station and mobile station
regardless of their positions in the network Choice and configuration of antenna system plays an important role
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Fundamental Fundamental Antenna Antenna
CharacteristicsCharacteristics
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Radiated PowerRadiated Power
Mean power received at any large distance is calculated by the Friis free-space equation:
Pt = transmitted power Pr(d) = received power, a function of transmitter-receiver distance Gt = transmitter antenna gain Gr = receiver antenna gain d = transmitter-receiver separation in meters L = miscellaneous loss factor for loss not related to propagation
L = 1 means no loss L > 1 means loss
λ = wavelength in meters
Ld
GGPdP rtt
r 22
2
)4()(
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Antenna BandwidthAntenna Bandwidth
Range of frequencies radiated where lowest and highest frequencies have radiated power that is 3 dB less than the radiated power at frequency with maximum power, f(max) Upper frequency, f(up), is frequency above f(max) where power
is 3 dB lower than f(max) Lower frequency, f(low), is frequency below f(max) where
power is 3 dB lower than f(max)
As a percent, B(p), of center frequency, f(ctr)
%100
ctr
lowupp f
ffB
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Antenna GainAntenna Gain
Ratio of antenna’s maximum radiation intensity to maximum radiation intensity from a reference antenna with same input power dBi – If reference antenna is isotropic source of 100% efficiency dBd – If reference antenna is simple dipole of typical efficiency
Gdip (gain with respect to dipole antenna) is 2.15 dB less than Gi (gain with respect to isotropic antenna)
Antenna gain, Gant, is a function of wavelength
Ae = Effective antenna area
2
4
e
antA
G
physicalape AA
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Antenna Beam WidthAntenna Beam Width
Antenna achieves gain by concentrating its radiation pattern in a certain direction The greater the gain, the narrower the beam width
Beam width is width of radiated pattern where signal strength is one-half that of maximum signal strength At this point, signal is 3 dB less than that of the maximum Angle between left and right points that are 3 dB down from
maximum is beam angle or beam width
For unidirectional antennas, resulting major lobe of radiation pattern has a certain width Common beam widths for cellular antennas: 60º, 90º, and 120º.
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Antenna Front-Back Antenna Front-Back RatioRatio
Measure of antenna’s ability to focus radiated power in intended direction successfully And not interfere with other antennas behind it
Referred to as f-b ratio or f/b ratio Ratio of radiated power in intended direction to radiated
power in opposite direction Ratio of the two gains is the f/b ratio:
180
0
P
P ratio f/b
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Frequency Re-UseFrequency Re-Use
7
61
23
4
5
7
61
23
4
5
7
61
23
4
5 Same frequencies used repeatedly in all directions Ability to radiate power in desired direction is critical
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Antenna Radiation Antenna Radiation PatternsPatterns
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Isotropic Radiation PatternIsotropic Radiation Pattern
Characteristics Completely non-directional antenna Radiates and receives equally well in all directions Theoretical point source or receiver Radiation pattern is spherical
Exists only as a mathematical concept There is no preferential radiation in one direction
Used as a reference to specify gain of a practical antenna
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Omnidirectional Radiation Omnidirectional Radiation PatternPattern
Horizontal Pattern Vertical Pattern
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Unidirectional Radiation Unidirectional Radiation Pattern Pattern
Horizontal Pattern Vertical Pattern
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Radiated Power ComparedRadiated Power Compared
2.15dB
dBi
dBd
Practical antenna
Theoretical halfwave dipole antennaIdeal isotropic radiator
2.15dB
dBi
dBd
Practical antenna
Theoretical halfwave dipole antennaIdeal isotropic radiator
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Properties of Properties of Unidirectional Unidirectional AntennasAntennas
Provide increased gain in a limited direction
Multiply use of separate channels by virtue of enabling sectorization
Do not overcome major disadvantages of omnidirectional antennas such as co-channel interference
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Antenna PolarizationAntenna Polarization
Polarization is an important property of a radio wave Radio waves have magnetic field H & electrical field E Orientation of electrical field determines polarization
If electrical field is vertical, radio wave is polarized vertically If electrical field is horizontal, radio wave is polarized
horizontally
Antenna of receiver should be oriented in same direction as polarization of transmitter antenna
Mobile antennas should be in the same orientation for best reception This is not always possible with hand-held phones
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Voltage Standing Wave Voltage Standing Wave Ratio (VSWR)Ratio (VSWR)
Ratio of maximum voltage to minimum voltage of standing wave along transmission line
Measure of impedance match between antenna and transmission line or coaxial cable The closer VSWR is to one, the greater
the efficiency of electrical power transfer
Formula Pr = Power, reflected
Pi = Power, incident
i
r
i
r
PP
1
PP
1
VSWR
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Antenna TypesAntenna Types
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Radiation Pattern of Half-Radiation Pattern of Half-wave Dipole Antennawave Dipole Antenna
3-D view Vertical section Horizontal section
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Omnidirectional AntennasOmnidirectional Antennas
Omnidirectional antenna Hertz antenna
1
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Marconi AntennaMarconi Antenna
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Omnidirectional Antenna Omnidirectional Antenna LimitationsLimitations
Radiates and receives equally well in all directions in the horizontal plane Signal power spread uniformly and only small percentage of
radiated power reaches receiver
Receiving antenna receives signals equally well from all directions in horizontal plane For mobile transmitter to be distinguished, it must be stronger
than other signals and the background noise
Limited bandwidth efficiency Very limited re-use of frequencies in adjoining areas
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Radiating Coaxial Cable Radiating Coaxial Cable AntennaAntenna
RF in from transmitter RF out (terminated)
Protective sheath
Outer conductorwith holes
Dielectric
Inner conductor
Radiating Coaxial Cable Antenna
Radiating Cable Radiation Pattern
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Multi-antenna SystemMulti-antenna SystemExamplesExamples
Pair of directional antennas mounted in different directions Radiation patterns point in opposite directions
Series of antennas around a given building Used when omnidirectional antennas would not be effective
Series of antennas located on the side of a building Minimizes interference with other receivers
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Panel AntennasPanel Antennas
Transmitter
Substrate
Radiatingpanel
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Unidirectional AntennasUnidirectional Antennas
Referred to as beam antennas Focus beams in one direction Concentrate radiated power into a beam while
minimizing emission in other directions Classifications:
Linear Logarithmic Parasitic
Broadband antenna
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Unidirectional AntennasUnidirectional Antennas
Traveling-wave Wire Antenna Folded Dipole Antenna Turnstile Antenna Loop Antenna Rhombic Antenna Yagi-Uda Antenna Log Periodic Antenna Mobile Antenna Sector Antenna
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Traveling-wave Wire Traveling-wave Wire AntennaAntenna
Reflectedwave
Dipoleantenna
Incidentwave
Resonant wave of wavelength antenna
Reflectedwave
Incidentwave
Antenna
Traveling wave for non-simple antenna
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Folded Dipole AntennaFolded Dipole Antenna
Beam
Driven elementlength =
Reflectorlength2 + 5%
Folded Dipole
Radiation patternFolded dipole antenna
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Turnstile AntennaTurnstile Antenna
Turnstile antenna Radiation pattern
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Loop AntennaLoop Antenna
Loop antenna Radiation pattern in
horizontal plane
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Rhombic AntennaRhombic Antenna
L L
LL
800 Preferred direction of radiation
L L
LL
800
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Rhombic Antenna Rhombic Antenna Radiation PatternRadiation Pattern
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Yagi-Uda AntennaYagi-Uda Antenna
Yagi-UdaAntenna
Director
Driven element
Reflector
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Yagi-Uda AntennaYagi-Uda Antenna
Beam
Directorlength = 2 - 5%
Driven elementlength = /2
Reflectorlength2 + 5%
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Log Periodic AntennaLog Periodic Antenna
All elements driven by transmitter
All elements driven but not active at same frequency
Has broad frequency response
Operates on more than one frequency
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Mobile Antennas: Collinear Mobile Antennas: Collinear Gain AntennaGain Antenna
Low-gain antenna
Two types
- Through-the-glass
- Standard mount
Have upper and lower portion
separated by phase matching coil
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Sector AntennasSector Antennas
120º
60º
60º
3-sector cell 6-sector cell
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Sector AntennasSector Antennas
Realistic antenna coverage in 6-sector cell
Antenna overlap in 6-sector cell
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Antenna Configuration Antenna Configuration RequirementsRequirements
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Antenna Configuration Antenna Configuration RequirementsRequirements
Antenna separation Diversity Isolation Interference Radiation patterns not distorted by obstacles or
reflections
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Space DiversitySpace Diversity
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Polarization DiversityPolarization Diversity
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IsolationIsolation
Needed to avoid distortion due to intermodulation Need to fulfill these isolation values
TX – RX isolation > 30 dB TX – TX isolation > 30 dB
Horizontal physical separation requirements 30 dB isolation: 11.5 λ 800 MHz: 10 feet 1900 MHz: 6 feet
Vertical separation requirement for antenna is 0.2 meter
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Antenna DowntiltAntenna Downtilt
Beam of vertically-mounted antenna
Beam of vertically-mounted- antenna with tilted beam
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Antenna HeightAntenna Height
Reducing antenna height by 50% will reduce average received signal by 6 dB
Repositioning transmit and/or receive antenna can help maintain system balance
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Signal Coverage ProblemsSignal Coverage Problems
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 57
Signal Coverage ProblemsSignal Coverage Problems
Design problems Maintenance problems System maturation Site location and geometry Shadows in pattern Nulls in pattern Intermodulation, co-channel, and adjacent channel
interference problems
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Resolving Signal Coverage Resolving Signal Coverage ProblemsProblems
Reduce antenna height
Downtilt the antenna
Use higher or lower gain antenna
Use antenna with wider or narrower horizontal or vertical beam width
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Return Loss of an AntennaReturn Loss of an Antenna
Power difference between incident and reflected wave in transmission line feeding the antenna
3 dB return loss means reflected power is half of incident power
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InterferenceInterference
Multipath condition
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InterferenceInterference
time
Sig
na
l Am
plit
ud
e
+
-
Non-fade period
Fading
Rayleigh fading
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Co-Channel InterferenceCo-Channel Interference
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Advanced System Advanced System AntennasAntennas
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Advanced Antenna Advanced Antenna SystemsSystems
Are expensive Increase cell coverage and capacity without building
additional sites Examples
Multi-beam antenna systems Smart antenna systems
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Multi-Beam AntennasMulti-Beam Antennas
Standard cell divided into 18 microsectors
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Smart Antenna SystemsSmart Antenna Systems
Fixed Beam Strategy Adaptive Beam Strategy
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Smart Antenna SystemsSmart Antenna Systems
Time division duplex (TDD) communication systems transmit and receive on same frequency
Frequency division duplex (FDD) transmit and receive on separate frequencies
Capacity for frequency reuse is greater than a standard cell system
Power needed for radio beam is less than for fixed beam strategy
Use code division multiple access method to balance the traffic load
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 68
Traffic Load Balancing Traffic Load Balancing Smart Antenna SystemsSmart Antenna Systems
Cell with unbalanced load
Cell with balanced load
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Handling Capacity of Handling Capacity of Smart Antenna SystemsSmart Antenna Systems
Adaptive area
Switched beam area
Conventionalsectorization area
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Switched Beam versus Switched Beam versus Adaptive Array SystemsAdaptive Array Systems
Factors to consider Interference suppression Range and coverage Spatial division multiple access (SDMA)
Enables wireless system to efficiently use available frequencies where customers are located
Creates a sector for each receiver while maximizing signal strength at receiver and minimizing interference
Uses multiple antennas to combine signals in space at location of receiver
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Antenna Covers and Antenna Covers and Support StructuresSupport Structures
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Antenna Covers and Antenna Covers and Support StructuresSupport Structures
Antenna covers Protect antenna element from weather Make antenna more aesthetically pleasing
Types of support structures Self-supporting towers Guyed towers Monopole Camouflaged towers Existing structures
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Antenna Support Antenna Support StructuresStructures
Self-supporting towers Large 3-D framework of galvanized girders Antenna may be placed at top or any level of tower based on
transmission requirements
Guyed towers Made of crisscrossing steel girders Held in place by guy wires that form a 15 degree vertical angle Antenna may be placed at top or any level of tower based on
transmission requirements
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 74
Antenna Support Antenna Support StructuresStructures
Monopole with 3-sector head
Requires less land area and is more aesthetically pleasing than other structures
• Antenna placement depends on transmission requirements
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 75
Antenna Support Antenna Support StructuresStructures
Camouflaged towers Existing support structure
Buildings Water towers Electric towers Light pole Highway signs
FAA identifies special lighting and/or safety requirement FCC specifies power allowed based on various factors
Terrain Frequencies used Other radio uses in the area
June 2001 Copyright 2001 Global Wireless Education Consortium RT-RFA 76
Industry ContributorsIndustry Contributors
AT&T Wireless (http://www.attwireless.com) Ericsson (http://www.ericsson.com) LCC International, Inc. (http://www.lcc.com) Motorola (http://www.motorola.com) Nortel Networks (http://www.nortel.com) Northeast Center for Telecommunications
Technologies(http://nctt.org/index2.htm) RF Globalnet (http://www.rfglobalnet.com)
The following companies provided materials and resource support for this module:
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Industry Contributors, Industry Contributors, cont.cont.
Space 2000 (http://www.cdmaonline.com) Telcordia Technologies, Inc (http://www.telcordia.com) Verizon (http://www.verizon.com)
The following companies provided materials and resource support for this module:
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Individual ContributorsIndividual ContributorsThe following individuals and their organization or institution provided materials, resources, and development input for this module: Dr. Chaouki Abdallah
University of New Mexico http://www.unm.edu
Dr. Jamil Ahmed British Columbia Institute of Technology http://www.bcit.ca
Dr. John Baldwin South Central Technical College http://[email protected]
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Individual Contributors, Individual Contributors, cont.cont.
Dr. Derrek Dunn North Carolina A&T State University http://www.ncat.edu
Mr. Robert Elms ACRE Engineering Services http://[email protected]
Mr. Stuart D. MacPherson Durban Institute of Technology
Dr. James Masi Springfield Technical Community College http://www.stcc.mass.edu/nsindex.asp
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Individual Contributors, Individual Contributors, cont.cont.
Ms. Annette Muga Ericsson http://www.ericsson.com
Dr. Dave Voltmer Rose-Hulman Institute of Technology http://www.rose-hulman.edu