13 CDMA Antenna System-48

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



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Main Content


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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Documents

13 CDMA Antenna System-48