Antennas for CDMA System
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Antennas for CDMA System
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第 2 页
Contents
Base station antenna specification and meanings
Antenna types and trends
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Technical Data
B lah
blahb la h bl ah
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第 4 页
Electrical properties Operation Frequency Band Input impedance VSWR Polarization Gain Radiation Pattern Horizontal/Vertical beamwidth Downtilt Front/back ratio Sidelobe suppression and null filling Power capability 3rd order Intermodulation Insulation
Mechanical properties Size Weight Robe material Appearance and color Working temperature Storage termperature Windload Connector types Package Size Lightening
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Electrical properties
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Wavelength
1/2 Wavelength
1/4 Wavelength
1/4 Wavelength
1/2 Wavelength
Dipole
Dipoles
1900MHz : 157mm
800MHz : 375mm
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1 个 dipole (received power) : 1mW
Multiple dipole matrixReceived power : 4 mW
GAIN= 10log(4mW/1mW) = 6dBd
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Gain=10log(8mW/1mW) = 9dBi
“Sector antenna”Received power : 8mW
Omnidirectional array”Received power : 1mW
(Overlook
Antenna
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第 9 页
Frequency Range
CDMA(CELLULA ) 800 MHz: 824-894MHz
CDMA(PCS/PCN) 1900 MHz: 1850-1990MHz
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Impedance
50
Cable
50 ohms
Antenna 50 ohms
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9.5 W80
ohms50 ohms
Forwarda: 10W
Backward: 0.5W
Return Loss : 10log(10/0.5) = 13dB
VSWR (Voltage Standing Wave Ratio)
VSWR
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1.5=(VSWR-1)/(VSWR+1)RL=-20lg
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第 13 页
Polarization
Vertical Horizontal
+ 45degree slant - 45degree slant
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V/H (Vertical/Horizontal) Slant (+/- 45°)
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Linear,verticaldual linear 45 slant
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Dipole
Ideal radiating dot source(lossless radiator)
eg: 0dBd = 2.15dBi
dBd and dBi
2.15dB
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Pattern
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Beamwidth
120° (eg) Peak
Peak - 10dB
Peak - 10dB
10dB Beamwidth
60° (eg) Peak
Peak - 3dB
Peak - 3dB
3dB Beamwidth
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3dB Beam width Horizontal
Directional Antenna : 65°/90°/105°/120 °Omni : 360°
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3dB Beam width Vertical
Directional : Omni-directional :
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Down Tilt
Mechanical down tiltFixed electronic down tiltAdjustable electronic down tilt
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Demonstration of Electronic Down-tilt
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Non down tilt Electronic downtilt Mechanical downtilt
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第 25 页
Front to Back Ratio
Ratio of maximum mainlobe to maximum sidelobe
F/B = 10 log(FP/BP) typically : 25dB
Back power Front power
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第 26 页
Upper Side lobes Suppression & Null Fill
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第 27 页
Sidelobes
DOWN SIDELOBE (dB)
UP SIDELOBE (dB)
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Permitted Power
Continuous :25-1500watts
peak :n2p
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1000mW ( 1W) 1mW
10log(1000mW/1mW) = 30dB
Isolation
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Mechanical properties
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Dimensions
LWHLength : connected with vertical bandwidth and
gainWidth : connected with horizontal bandwidthHeight : connected with techniques adopted
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Weight
Affecting transmission and deploy
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Radome Material
PVC, FiberglassAnti-temperature 、 water-proof , anti-
aging , weather resistant
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ColourGood-looking,
environment-protecting
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Operating Temperature Range
Typical range : -40°C — +70°C
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Storage Temperature Range
Typically : -40°C — +70°C
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Wind Load
Eg: 83N at 160 km/h
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第 41 页
Connector Type
7/16”DIN , N , SMA female
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Mast
Mast diameter 45-90mm
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Lightening Protection
Direct Ground
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第 44 页
Antenna Systems
Antenna systems include more than just antennas Transmission Lines
necessary to connect transmitting and receiving equipment Other Components necessary to achieve desired system function
Filters, Combiners, Duplexers - to achieve desired connections Directional Couplers, wattmeters - for measurement of performance
Manufacturer 抯 system may include some or all of these items remaining items are added individually as needed by system operator
F R
Duplexer
Comb-iner
BPF
TX
RX
TXTransmission LineJumper
Jumpers
DirectionalCoupler
Antenna
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第 45 页
Characteristics of Transmission Lines
FoamDielectric
AirDielectric
Typical Coaxial CablesUsed as Feeders in Wireless Applications
Physical CharacteristicsType of Line
coaxial, stripline, open-wirebalanced, unbalanced
Physical ConfigurationDielectric:
airfoam
Outside Surface:unjacketedjacketed
special: plenum rated
Size (nominal outer diameter)1/4?1/2? 7/8? 1-1/4? 1-7/8? 2-
1/4? 3
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Characteristics of Transmission Lines
Electrical Characteristics Attenuation:
varies with frequency, size, dielectric characteristics of insulation
usually specified in db/100 ft and/or db/100 m
Characteristic Impedance ZO (50 ohms is the usual commercial standard; 75 sometimes used) value set by inner/outer diameter ratio and d
ielectric characteristics of insulation connectors must preserve constant impedanc
e (see figure at right) Velocity Factor
determined by dielectric characteristics of insulation.
Power-Handling Capability varies with size, conductor materials, dielect
ric characteristics
dD
Characteristic Impedance of a Coaxial Line
Zo = ( 138 / ( 1/2 ) ) Log10 ( D / d )
= Dielectric Constant = 1 for vacuum or dry air
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Transmission Lines:Special Electrical Properties
Transmission lines have impedance-transforming properties When terminated with same impeda
nce as Zo, input to line appears as impedance Zo
When terminated with impedance different from Zo, input to line is a complex function of frequency and line length. Use Smith Chart or formulae to compute
Special case of interest: Line section one-quarter wavelength long has convenient properties useful in matching networks ZIN = (Zo
2)/(ZLOAD)
Zo=50ZLOAD=
50ZIN = 50
Matched Condition
Zo=50ZLOAD=
83-j22
ZIN = ?
Mis-Matched Condition
Zo=50ZLOAD=
100ZIN=25
/4
ZIN= ZO2
/ ZLOAD
Deliberate Mis-Matchfor Impedance Transformation
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Transmission Lines:Some Practical Considerations
Transmission Lines: Some Practical Considerations Periodicity of inner conductor supportin
g structure can cause VSWR peaks at some frequencies, so specify the frequency band when ordering
Air dielectric lines: lower loss than foam-dielectric; dr
y air is excellent insulator shipped pressurized; do not accept
delivery if pressure leak Foam dielectric lines
simple, low maintenance; despite slightly higher loss
small pinholes and leaks can allow water penetration and gradual attenuation increases Foam
Dielectric
AirDielectric
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第 49 页
MAIN FEEDER
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JUMP CABLE
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第 51 页
7DIN CONNECTOR
DIN & N CONNECTOR
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Lightening Arrestor
Rf port 2
Grounding
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ACCESSORIESTrimming Tool or Hand Tool KitClampEarthing KitWall GlandsHoisting StockingUniversal Ground Bar
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Antenna
7/16 Din Connector
7/8“ Cable
Grounding
1/2“ Jumper
Cabinet
EMPGrounding clip
Grounding bar
1/2 Clamp
Tower Top Amplifier
7/8“ Cable
Machine house
1/2 Jumper
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Transmission Lines:Important Installation Practices
Respect specified minimum bending radius! Inner conductor must remain
concentric, otherwise Zo changes
Dents, kinks in outer conductor change Zo
Don 抰 bend large, stiff lines (1-5/8?or larger) to make direct connection with antennas. Use appropriate jumpers, weatherproofed properly. Secure jumpers against wind vibration.
ObserveMinimumBendingRadius!
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Transmission Lines:Important Installation Practices
During hoisting, allow line to support its own weight only for distances approved by manufacturer. Deformation and stretching may result, changing the Zo. Use hoisting grips, messenger cable
After mounting, support the line with proper mounting clamps at manufacturer 抯 recommended spacing intervals. Otherwise, strong winds will set up damaging metal-fatigue-inducing vibrations
200 ft~60 MMax. 3-6 ft
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第 57 页
RF Filters: Types and Applications
Filters are the basic building blocks of duplexers and more complex devices
Most manufacturers network equipment includes internal bandpass filters at receiver input and transmitter output
Filters are also available for special applications
number of poles (filter elements) and other design variables determine filter抯 electrical characteristics bandwidth, rejection, insertion lo
ss, slopes, losses, ripple, etc.
Notice construction: RF input excites one quarter-wave element and electromagnet fields propagate from element to element, finally exciting the last element which is directly coupled to the output.
Each element is individually set and forms a pole in the filter 抯 overall response curve.
Typical RF Bandass Filter
/4
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RF Filters: Basic Characteristics & Specifications
Types of Filters Single-Pole:
Pass Reject (notch)
Multi-pole: Band-Pass Band-Reject
Key Electrical Characteristics insertion loss passband ripple passband width
upper, lower cutof f frequencies attenuation slope at band edge ultimate out-of-band attenuation
Typical bandpass filters have insertion loss of 1-3 dB. and passband ripple of 2-6 dB.
Bandwidth is typically 1-20% of center frequency, depending on application. Attenuation slope and out-of-band attenuation depend on # of poles & design
Typical RF Bandass Filter
0
Att
enu
atio
n,
dB
Frequency, MegaHertz
passband rippleinsertion loss
-3 dB passbandwidth
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Typical Tuned Combiner Application
Basics of Transmitting Combiners
Purpose: Allow multiple transmitters to feed single antenna, and provide: minimum loss from transmitter to antenn
a maximum isolation between transmitters
Types: Tuned
low insertion loss ~1-3 dB transmitter frequencies must be signi
ficantly separated Hybrid
insertion loss -3 dB per stage no restriction on transmitter frequen
cies Linear Amplifier
linearity and intermodulation are major design & operation issues
TX TX TX TX TX TX TX TX
Antenna
Typical Hybrid Combiner Application
TX TX TX TX TX TX TX TX
Antenna
~-3 db
~-3 db
~-3 db
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第 60 页
Combiners: CDMA Considerations
CDMA operators will want to combine multiple CDMA carriers into single antennas; combiners will be needed
Tuned Combiner Technique must use multi-pole bandpass filters adjacent-frequency CDMA carriers prob
ably cannot be combined using this technique alone
Hybrid Technique substantial insertion loss will limit numb
er of carriers per antenna to perhaps 4 if technique used alone
Composite method using staggered tuned combiners and hybrid combiners, and/or
Linear amplifiers will probably be exploited for high-density CDMA BTS configurations in the future
Composite Method:Tuned & Hybrid
f4 f6f5f1 f7f3 f8f2
Hybrid Combiner
One Operator 抯 CDMA Carriers
Antenna
Linear Amplifier Method
f4 f6f5f1 f7f3 f8f2
Linear Amplifier
One Operator 抯 CDMA Carriers
Antenna
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第 61 页
Duplexer Basics
Duplexer Purpose: allow simultaneous transmitting and receiving on one antenna Zte 1900 MHz BTS RFFEs include i
nternal duplexer Zte 800 MHz. BTS does not include
duplexer but commercial units can be used if desired
Important Duplexer Specifications TX pass-through insertion loss RX pass-through insertion loss TX-to-RX isolation at TX freq. (RX
intermodulation issue) TX-to-RX isolation at RX freq. (TX
noise floor issue) internally-generated intermod limit s
pecification
fR fT
RX TX
Antenna
Duplexer
Principle of Operation
Duplexer is composed of individualbandpass filters to isolate TX fromRX while allowing access to antennafor both. Filter design determinesactual isolation between TX and RX,and insertion loss TX-to-Antenna and RX-to-Antenna.
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第 62 页
Directional Couplers
This device measures forward and reflected energy in a transmission line. It has 4 ports: Input (from TX), Output (to load) Forward, Reverse Samples
Sensing loops probe E& I in line equal sensistivity to E & H fields terminations absorb induced curren
t in one direction, leaving only sample of other direction
Typical Performance Specs: Coupling factor ~20, ~30, ~40 db.,
order as appropriate for application Directivity ~30-~40 dB., f($)
defined as relative attenuation of unwanted direction in each sample
Principle of Operation
ZLOAD= 50
Input
Reverse Sample
Forward Sample
RT
RT
Typical Directional Coupler
Main line E & I induce equal signals in sense loops. E is direction-independent, but the polarity depends on direction andcancels sample induced in one direction.Thus sense loop signals are directional.One end is used, the other terminated.
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第 63 页
Return Loss and VSWR Measurement
A perfect antenna will absorb and radiate all the power fed to it. Real antennas absorb most of the power, but reflect a portion back down t
he line. A Directional Coupler or Directional Wattmeter can be used to measure t
he magnitude of the energy in both forward and reflected directions. Antenna specs give maximum reflection over a specific frequency range. Reflection magnitude can be expressed in the forms VSWR, Return Loss,
or reflection coefficient. VSWR = Voltage Standing Wave Ratio
Transmission Line
AntennaDirectionalCoupler Fwd
Refl
RFPower
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第 64 页
Return Loss and VSWR Calculations
Forward Power, Reflected Power, Return Loss, and VSWR are related by the following equations and the graph. Typical antenna VSWR specifi
cations are 1.5:1 maximum over a specified band.
VSWR 1.5 : 1
= 14 db return loss
= 4.0% reflected power
VSWR vs. Return Loss
VSWR
0
10
20
30
40
50
1 1.5 2 2.5 3
VSWR =
Reflected PowerForward Power
Reflected PowerForward Power
1 +
1 -Reflected PowerForward Power
ReturnLoss, dB = 10 x Log10 ( )
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第 65 页
Thank you