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7/31/2019 13 CDMA Antenna System-48
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Antennas and Feeder System
ZTE University
CDMA-BSS Team
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Main Content
BTS Antenna System Structure
BTS Antenna Specification and Meanings
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Cabinet
Antenna
7/16 Din Connector
7/8 Cable
Grounding
1/2 JumperEMP Grounding clip
Grounding bar
1/2 Clamp
Tower TopAmplifier
7/8 Cable
Machine house
1/2 Jumper
BTS Antenna System Structure
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Main Content
BTS Antenna System Structure
BTS Antenna Specification and Meanings
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Blah blahblah bl ah
What is the Antenna?
n An antenna is just a passive conductor carrying RF current: RF power causes current to flow in the antenna
current flowing radiates electromagnetic fields
electromagnetic fields cause current in receiving antennas
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Antenna Specifications and Meanings
n Electrical properties Halfwave Dipole Antenna Operation Frequency Band Antenna Gain Radiation Pattern
Horizontal/Vertical BeamwidthRadiation Pattern Downtilt Front/Back Ratio Sidelobe Suppression and Null
Filling Input Impedance VSWR Polarization Isolation
n Mechanical properties
Size
Weight
Radome material
Appearance and color Working temperature
Storage temperature
Windloading
Connector types
Package Size
Lightning Protection
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Electrical Properties
Antenna should be testedstrictly in the lab before
selling.
We make the choiceaccording to ourrequirement
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Wavelength
1/2 Wavelength
1/4 Wavelength
1/4 Wavelength
1/2 Wavelength
Dipole
1900MHz 157mm800MHz 375mm
Antenna Foundation:Halfwave Dipole
n Halfwave dipole is a classic antenna and it is very popular. It can be usedindependently, or multiple dipoles can be combined together into an
antenna matrix.
n A halfwave dipole has two symmetrical arms, one arm is wave length of
the radio frequency signal.
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TX RX
Width of band denotes current
magnitude
Zero current at each end
Maximum current at the middle
Current induced in receiving antenna is vector sum of
contribution of every
tiny lice ?of radiating antenna
each tiny imaginary lice of the antenna does its share
of radiating
Antenna Foundation:Halfwave Dipole
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1 dipole(received power) 1mW
Multiple dipole matrixReceived power 4 mW
GAIN = 10log(4mW/1mW) = 6dBd
Halfwave Dipole Radiation Pattern
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Antenna Working Frequency Range
n Both transmitting and receiving antenna can only work in a
specific frequency range.
n Antenna frequency range is defined as the frequency
bandwidth, in which the antenna gain drops less than 3 dBand the VSWR is 1.5 .
n Generally, antenna performance for different frequencies
within the band varies a little, but its acceptable.
n CDMA(CELLULAR 800 MHz: 824 - 894MHz
n CDMA(PCS) 1900 MHz: 1850 - 1990MHz
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Working Frequency Range ( BANDWIDTH )
896 - 824 = 72MHz
(Decided by antenna manufacturer, and laboratory tests)
Optimum 1/2 wavelengthfor dipole at 860MHz
at896
MHzAntennaDipole
at824
MHz
Antenna Working Frequency Range
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Antenna Gain
Attention: Antennas are passive devices; they do NOT amplify RF energy.
What is antenna gain?
On the condition of same inputpower and same position ofspace, the ratio between thepower radiated from thepractical antenna and from theideal isotropic antenna iscalled the antenna gain.
Same amount ofenergy, focussed in a
particular direction
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Halfwave dipole
Ideal Isotropic antenna
eg: 0dBd = 2.15dBi
2.15dB
Gain Calculation: dBd and dBi
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Gain Calculation: dBd and dBi
Isotropic vs. Dipole
PLAN VIEW
isotropic
dipole
dB Gainref Dipole (dBD)
dB Gainref isotropic (dBi)
0dBi(ref)
0dBD(ref)
DirectionalAntenna
Azimuth Pattern
G =s1 /s0 unit dBi
G == s1 / GA0 unit:dBd
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ERP and EIRP
n Effective Radiated Power (ERP and EIRP) apparent power in a particular direction. It is equal to
actual transmitter power times antenna gain in thatdirection.
Radiated power = Input power x antenna gain
or in dB = dBm + dB(i or d)
eg:50dBm + 4.4 dBiEIRP = 54.4 dBm (right picture)
n ERP is expressed in comparison to a standard radiator ERP: compared with dipole antenna EIRP: compared with isotropic antenna
A
B
EIRP B A (ref)
100w275w
ReferenceAntenna
TX100 W
A
DirectionalAntenna
TX100 W
B
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Base StationTransmitter(20 watts)
Convert to dBm10Log(20) + 30 = +43 dBm
jumper
HeliaxCable
jumper
-0.5dB
-0.5dB
-3dB
Antenna Gain= + 18 dBi
Ant InputPower = + 39dBm
EiRP = +39 + 18 = +57 dBm
Antenna Gain Example
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Antenna Radiation Pattern
n The first basic function of antenna is to radiate energy toouter space.
n The second basic function is to radiate most of energy tothe desired direction.
n But in fact, the practical radiation is very complex, it iscalled: radiation pattern
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60 (eg) Peak
Peak - 3dB
Peak - 3dB
3dB Beamwidth
Beamwidth
n The radiation pattern has several lobes; the strongest is called themain lobe and the others are side lobes.
n From the peak of the main lobe, the radiation will become weaker
and weaker as it spreads to the side. The angle between two
position which is 3dB below the peak is called beamwidth or half-
power angle.
n The narrower the beamwidth, the better of concentration of the
radiation and the higher of the gain.
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Horizontal 3dB Beamwidth
n Directional Antenna 65 /90 /105 /120 Omni
360
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Typical 903dBbeamwidthsketch map
Horizontal 3dB Beamwidth
n
20 ,30 beamwidth antennas are mostly used in narrowareas such as a highway 65 are usually used in city
area 90 s are used more in suburbs and countryside.
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Directional Omni
Vertical 3dB Beamwidth
n
48 ,33 ,15 ,8 are some common values for thevertical 3dB beamwidth.
n If the vertical beamwidth is small, then we can control the
coverage by adjusting the downtilt.
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Antenna Downtilt
n Mechanical Downtilt
Physically tilt the antenna. The pattern in
front goes down, and behind goes up.
This is
popular for sectorization and special omni
applications
n Electrical Downtilt (fixed and adjustable)
Incremental phase shift is applied in the
feed network
the pattern droops all around, like an
inverted saucer common technique when downtilting omni
cells
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Non down tilt Electronic downtilt Mechanical downtilt
Different Downtilt Effects
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Downtilt Adjustment
n In general, the original downtilt can be calculated = arctan (h/R) A/2 antenna downtilt hantenna height
Rcell coverage radius A---antenna vertical 3dB beamwidth
n In this formula, the main lobe of antenna will point tothe edge of cell coverage.
n Actually, the antenna will often need downtiltadjustment during optimization to ensure the realcoverage does not go too far or too near.
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Front/Back = 10 log(FP/BP) typically 18 to 30dB, the larger the better
Back power Front power
Back Power
(interference) Front Power
Front to Back Ratio
n Front-to-back ratio
Antenna front-to-back ratio measures how much energy is
radiated outside the antennas main beam.
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DOWN SIDELOBE(dB)
UP SIDELOBE ( dB)
Up Sidelobe Restraint
n Usually, the up sidelobe energy is not used. So we
perform restraint on the up sidelobe.
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Sidelobe Suppressionand Null Filling
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Cable
50 ohms
Antenna
50 ohms
Antenna Input Impedance
n When antenna and feeder cable are connected, the best condition (best
antenna efficiency) would be if their impedance are completely matched.
n There are four parameters that can be used to measure antenna efficiency,
these are;
n Reflectance, Traveling Wave Coefficient, VSWR, Return Loss
n VSWR and Return Loss is commonly used.
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9.5 W
80
ohms50 ohms
Forward: 10W
Backward: 0.5W
Return Loss 10log(10/0.5) = 13dB
VSWR (Voltage Standing Wave Ratio)
Voltage Standing Wave Ratio
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VSWR Characteristics
n Impedance and Voltage Standing Wave Ratio (VSWR) / Return
Loss
Input impedance of the antenna must match the characteristic
impedance of the transmission line
Otherwise, a reflected wave is generated, directed back towards theenergy source.
The ratio between the maximum and minimum voltage is defined as
the Voltage Standing Wave Ratio (VSWR).
Ant VSWR = 1.5:1Return Loss = 20 Log VSWR +1 = 14dBVSWR-1+40 dBm(10 watts)
+26 dBm
0dBi EIRP = +39.8 dBm
(400mW)
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Vertical Horizontal
+ 45degree slant- 45degree
slant
Antenna Polarization
n Polarization describes the orientation of the electric field
vector.
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V/H (Vertical/Horizontal) Slant (+/- 45 )
Dual Polarization Antenna
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Power TransferBetween Antenna A
and Antenna B
A B
A
B
Co-Polarized
Cross-Polarized
PolarizationDiscriminationFree-Space
Environment
Severe MultipathEnvironment
Maximum energy transferbetween Tx and Rx antennastakes place when the antennashave the same polarizationand spatial orientation.
Polarization Discrimination
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1000mW ( 1W) 1mW
10log(1000mW/1mW) =30dB
Antenna Port Isolation
n
In dual polarization antenna, complete port isolation is impossible.n If one port receives an input energy, some of the energy will provide
interference in the other port.
n In this example the isolation is 30dB, the higher the better.
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Antenna Mechanical Properties
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L W H
The Length is related to the vertical bandwidth and gain
The Width is related to the horizontal bandwidth
The Height is related with the techniques adopted
Antenna Dimensions
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Antenna weight affectstransmission and deployment
Antenna Weight
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Radome material may be PVC orFiberglass which are water-proof, weather-proof, and has anti-aging characteristics
Radome Material
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Some antennas are made verypleasing to look at or made to blendwith the environment
Appearance Color
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Operating Temperature Range
Typical range -40 C +70 C
Storage Temperature Range
Typically -40 C +70 C
Connector Type
7/16DIN N SMA female
Physical Parameters
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Mast
Mast diameter 45-90mm
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Lightning arrestersare directlyconnected to ground
Lightening Protection
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Main Feeder
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Jump Cable
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7/16DIN-F CONNECTOR
7/16DIN-M and N-M CONNECTOR
Connectors
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Feeder Installation Annex
n Trimming Tool or Hand Tool Kit
n Clamp
n Grounding Kit
n Wall Glands
n Universal Ground Bar
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