Sistem Komunikasi Bergerak 2

PT3163-SISKOMBER-MODUL:06

Modul : 05

PT3163SISTEM KOMUNIKASI BERGERAK

Antena pada Sistem Cellular

Program Studi D3 Teknik TransmisiJurusan Teknik Elektro – Institut Teknologi Telkom

BANDUNG, 2008


Macam-Macam Jenis Antena yang ada di BTS

1) Omnidirectional

Tx

Rx Rx

2) Sectoring 120o

3) Sectoring 60o

Pada kondisi awal biasanya digunakan pola omnidirectional ( tergantung demand ).

Kegunaan dari pola Sectoring a. Menambah

kapasitasb. Mengurangi

interferensi


Bentuk Konfigurasi Sektor Sel

4 sector ( quad sector )


RBS / BTS = Radio Base Station / Base Transceiver Station= Merupakan perangkat transceiver yang berhubungan dari / ke

pelanggan (Interface / repeater antara MS dan MSC) .= Elemen-elemen RBS :

Transceiver Control Unit / BSC / Base Station Controller Antena Data terminal

singleantenna

base stationhousingjalur transm isi

gelom bangm ikro m enujuBSC

site 3 sektor dengan 7array antena tiapsektornya

Bagaimana bentuk antena pada lokasi site ?


Karakteristik Antena pada Sistem SelularAntena pada BTS, mempunyai karakteristik :• Pola radiasi yang diinginkan mempunyai pola radiasi horizontal

ke segala arah, tetapi tidak mempunyai pola radiasi ke atas (vertical plane)

• Banyak digunakan antena dipole ( terutama dipole ½ )• Mempunyai daya pancar yang cukup tinggi.

Antena pada MS, mempunyai karakteristik :• Antena MS harus mempunyai pola radiasi kesegala arah

(omnidirectional).• Berdimensi kecil sehingga memungkinkan diletakkan dibody

handset.• Mempunyai daya pancar yang rendah.


Radio (Tx & Rx) System

• Signal Source: Informasi & Baseband Processing.• Tx-er: Modulator, Channel Encoder, Interleaver, etc.• PA: Power Amplifier.• Feedline: Cable, Connector and Jumper.• Pre-Amp: LNA.• Rx-er: Demodulator, Channel Decoder, De-Interleaver, etc.

RxerPASignalInformation

Txer

SignalSource(Voice, data, etc)

propagation

feedlineTx filter Rx filter Pre-Amp


Structure of Transmitter

• BB Processing: to process analog signal into digital signal & other processing• Mod: translate from BB freq. To RF freq depend on type of cellular system

being used e.g. G-MSK modulator for GSM.• Power Amp:

- Class A: high linearity- Class B: greater output power more efficient than Class A, but less linear- Class AB: combined adv. of class A & B become widely used in wireless.- Class C: more power efficient widely used in wireless

BBProcessing

Mod PAInfoSignal

Jumper

Jumper

Cable

Connector

Depend ontype of Mod used


Transmitting Combiners• Allows multiple transmitters to feed

single antenna, providing– Minimum power loss from transmitter

to antenna– Maximum isolation between

transmitters• Combiner types

– Tuned• low insertion loss ~1-3 dB• transmitter frequencies must be

significantly separated– Hybrid

• insertion loss -3 dB per stage• no restriction on transmitter

• frequencies– Linear amplifier– Linearity and intermodulation are

major design and operation issues


Reducing Cost with Combine Solution between AP and Antenna Indoor (Radio Interface)

Type AType B

With Amplifier


Generic Structure of Rxer

• Block diagram of Rxer varies depend on type of modulation, encoder, and/ or base band processing.

• Parameters to be considered are:- frequency range- dynamic range- sensitivity- distortion- noise- tuning speed

12...

N

ChanelEncoder

PAData/Signal

filter

jumper

Multicoupler/RF Distributor

X IF

LOfeedline

Antenna

IF

Rxer


• Antenna: to convert electromagnetic energy from atmosfer electric energy and transfer it to feed line

• Feed line

Receiver Components

Jumper Cable Jumper

• Filter & Pre-Amplifier:- Filter: to pass the wanted signal & attenuated the

interference designed to work according to the intended bands- Pre-Amplifier is used to increased S/N of received

signals.

= Connector

Jumper to ease maintenance and installation


Receiver Components

• Multicoupler:- used for RF distribution- many signals/users can share the same receive antenna:

1 : 4Splitter

1 : 4Splitter

# 1

# 2

# 3

# 4

1 : 4Splitter

# 13

# 14

# 15

# 16

RFin

signal


4 Basic Antenna System.

G=2.14 dBi

a. Dipole

G=4 dBi

b. monopole

Ground plane

c. Loop

Ground plane

conductorFeed point

d. Microstrip/ patch

dielectric


Base Station Antenna.• Use antenna with higher gain• Could be omnidirectional or sectoral depending on cell type• Collinear antenna:

S

2

2

4

feeder

line

OmnidirectionalRadiationPattern

boresight

main lobe

side lobe(elevation)


• Log periodic dipole array (LPDA)

Base Station Antenna.

DipolesTransmissionline

- BW is smaller than LPDA- typical gain 12 – 14 dB

Reflector Driven element (dipole)Directors

• Yagi antenna

Directional RadiationPattern

main lobe

main lobeside lobeback lobe

- very wide BW, with constant SWR- typical gain 10 dBi


Antenna Downtilt


Vertical Depression Angles


Types Of Downtilt


Antenna Downtilt: Reduce Interference


Antenna Downtilt: Avoid Overshoot


SWR of Antenna

• SWR = Vmax/Vmin, define the matching level between antenna and feeder line

• Reflection coefficient:

1

1

SWR

SWR2

2log10Re Lossturn

where represent a percent of reflected power defined by:

Amplitude

Vmax

Vmin


Performance Criteria of Antenna• Antenna Pattern, defined at azimuth and elevation orientation

either omni or bidirectional antenna• Main Lobe & Side Lobe, the lower side lobe the better resistance to

interference• Input Impedance, usually complex matching input ipedance and

feeder line impedance is very critical to have maximum power transfer from feeder to antenna

• Beamwidth, usually defined as angular separation where there is 3 dB reduction from bore-sight

• Directivity & Gain, is ratio of radiation intensity at wanted direction and coverage radiation intensity over all direction

• Bandwidth, define operating range of antenna, limited by SWR. A typical BW is for SWR 1:1.2 at the band edge.

• Polarization, defined by orientation of

E

DG .


Performance Criteria of Antenna

• Front to Back Ratio, is ratio between main lobe & back lobe, very impotant for directional antenna.

• Spatial diversity:

Rx2 Rx1

h

d

)(835

11feet

fx

hd

where f is in MHz


Antenna Installation

a) Tower

Tx

Rx1Rx2

d

b) Roof Top, Edge of Buildingc) Roof Top

d

Rx1

Rx2Tx

d

Rx1

Rx2Tx

d) Wall Mounting

sector 1 Rx1

Rx2

Tx2

3

d


Antenna Installation Tolerance• Apply to physical oriented & plumbness of its installation• For omnidirectional antenna, it is unnecessary. But for directi-

onal antenna it is very critical• Usually taken +/- 5% from antenna horizontal/azimuth pattern.

Azimuth/Horizontal Pattern Tolerance from Bore Sight

110O +/- 5.5o

92O +/- 4.5o

60O +/- 3.0o

40O +/- 2.0o

Table: Horizontal Antenna Tolerance


Antenna Isolation

a. vertical

y

Tx

Rx

ywhere

dBy

VI log4028

c. slant

y

angleslantwhere

dBHIHIVISIo

90

Tx Rx

x

b) horizontal

10

log2022

xwhere

dBx

HI

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