basic knowledge of antenna and antenna selection

Internal Use Only▲

Basic Knowledge of Antenna

and Antenna Selection

Edition: V1.0

Released by:

GSM Network Planning & Optimization Dept.

Engineering Service Division

ZTE Corporation

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements.

Training Materials

for GSM Network Planning & Optimization

Version Introduction

Versio

n

Date Writer Assessor Amendment records

V1.0 2007-07-01 Wang JinFu Chen Ni None

V1.1 2009-02-16 Fei AiPing Chen Ni Document standardization



Key words:

antenna basics、beam width、gain、tilt angle、circumstances、selection of antenna types

Abstract:

In this guidebook, theories of antenna、antenna parameters and related concepts and

definitions are mainly described. Besides, selection of antenna types under different

circumstances and antenna installation specifications are also introduced.

Abbreviation:

None

Reference:

<Antenna Rudiments> Internet

< Selection Flow of GSM Antenna Types > Guidebook for GSM Network Planning &

Optimization Dept., Engineering Service Division, ZTE Corporation



Contents

1 Overview of Antenna.........................................................................................................................1

1.1 General Development of BTS Antenna Technology.......................................................................1

1.2 Theories of Antenna Radiation........................................................................................................3

1.2.1 Electromagnetic Wave Radiation of Electric Dipole.............................................................3

1.2.2 Half-wave Dipole..................................................................................................................3

1.3 Internal Structure & Types of Mobile Communication BTS Antenna............................................4

1.3.1 Plate-shaped Directional Antenna.........................................................................................4

1.3.2 Isotropic Dipole Antenna with Series Feed...........................................................................9

2 Concepts & Meanings of Antenna Parameters.............................................................................11

2.1 Antenna Gain................................................................................................................................11

2.2 Directional Diagram of Radiation.................................................................................................12

2.3 Beam Width..................................................................................................................................12

2.3.1 Horizontal Beam Width.......................................................................................................12

2.3.2 Vertical Beam Width...........................................................................................................14

2.4 Frequency Band............................................................................................................................15

2.5 Polarization Mode.........................................................................................................................15

2.6 Down-tilt Mode.............................................................................................................................16

2.7 Antenna Front-to-back Ratio.........................................................................................................18

2.8 Antenna Input Impedance( Zin)....................................................................................................18

2.9 Antenna VSWR.............................................................................................................................19

2.10 Side Lobe Suppression & Null Fill...............................................................................................19

2.11 Third-order Intermodulation.........................................................................................................20

2.12 Isolation between Ports.................................................................................................................21

2.13 Case...............................................................................................................................................21

3 Measurement of Key Antenna Indicators Knowledge point......................................................22

3.1 Measurement of Antenna Gain......................................................................................................22

3.2 Measurement of 3dB Beam Width & Front-to-back Ratio............................................................22


I

3.3 Measurement of Antenna VSWR..................................................................................................23

3.4 Isolation Measurement of Dual-Polarized Antenna......................................................................24

3.5 Measurement of Intermodulation..................................................................................................24

4 Antenna Parameters........................................................................................................................26

4.1 Antenna Directional Angle............................................................................................................26

4.2 Antenna Height.............................................................................................................................27

4.3 Antenna Down-tilt........................................................................................................................29

5 Antenna Types..................................................................................................................................31

5.1 Antenna Types...............................................................................................................................31

6 Circumstances of Antenna Application..........................................................................................36

6.1 Dense Urban..................................................................................................................................37

6.2 Urban (Towns)..............................................................................................................................37

6.3 Suburb (Counties) & Villages.......................................................................................................38

6.4 Railways/ Highways (Roads)........................................................................................................38

6.5 Scenery Areas................................................................................................................................39

7 Selection of Antenna Type...............................................................................................................41

7.1 BTS antenna selection for urban...................................................................................................41

7.2 BTS antenna selection for suburb.................................................................................................41

7.3 BTS antenna selection for highway coverage...............................................................................42

7.4 BTS antenna selection for mountain area......................................................................................43

8 Installation & Modulation of Antenna...........................................................................................45

8.1 Antenna installation on Pole.........................................................................................................45

8.1.1 Installation pole must be straight.........................................................................................45

8.1.2 Lightening protection..........................................................................................................45

8.1.3 Diversity reception..............................................................................................................46

8.1.4 Antenna isolation.................................................................................................................47

8.2 Antenna Installation on Iron Tower..............................................................................................47

8.3 Summary.......................................................................................................................................48


II


Diagram Contents

Picture 1-1 Diagram of Relation between Doublet Angle and Radiation Power of

Electromagnetic Wave.....................................................................................................................3

Picture 1-2 Half-wave Dipole...........................................................................................................4

Picture 1-3 Half-wave Folded Dipole.............................................................................................4

Picture 1-4 Diagram of Directional Plate-shaped Antenna Appearing............................6

Picture 1-5 Vertically-set Line Array Formed by Several Half-wave Dipole..................6

Picture 1-6 Apply horizontally oriented theory by adding baffle-board to one side

the line array (take the line array of double half-wave dipole with baffle-

board as an example )............................................................................................................7

Picture 1-7 Directional plate-shaped antenna formed with several half-wave dipole8

Picture 1-8 Directional plate-shaped antenna consisting of several microstrip

dipole............................................................................................................................................9

Picture 1-9 Structure of plate-shaped directional antenna array......................................................9

Picture 1-10 Structure of Isotropic Dipole Antenna with Series Feed.............................................10

Picture 2-1 Diagram of antenna gain in dBi and dBd...........................................................11

Picture 2-2 Field strength diagram of isotropic antenna and directional antenna. 12

Picture 2-3 Diagram of horizontal beam width (3dB) of BTS antenna...........................................13

Picture 2-4 Diagram of BTS antenna coverage.....................................................................14

Picture 2-5 Diagram of BTS antenna vertical with 3dB beam width..............................14

Picture 2-6 Common polarization mode of BTS antenna...................................................16

Picture 2-7 Diagram of dual-polarization BTS antenna......................................................16

Picture 2-8 Diagram of BTS antenna down-tilt.......................................................................17

Picture 2-9 Comparison on BTS antenna down-tilt modes................................................17

Picture 2-10 Diagram of comparison between BTS antenna with or without null fill effect................20


III


Picture 3-1 Block diagram of measurement of antenna gain 、 half-power beam

width、front-to-back ratio、cross polarization discrimination.............................22

Picture 3-2 Block diagram of VSWR measurement...............................................................23

Picture 3-3 Block diagram of antenna isolation......................................................................24

Picture 3-4 Block diagram of antenna intermodulation measurement........................25

Picture 6-1 Dense urban..................................................................................................................37

Picture 6-2 Urban (towns).....................................................................................................................38

Picture 6-3 Suburb................................................................................................................................38

Picture 6-4 Railways & highways.........................................................................................................39

Picture 6-5 Scenery areas......................................................................................................................39

Picture 8-1 Solid diagram and vertical view of antenna.....................................................47


IV


Table Contents

Table 8-1 Horizontal diversity distance of antenna............................................................46


V


1 Overview of Antenna

Knowledge Point

In this chapter, the radiation theory of BTS antenna and its structure types are

described. In addition, antenna technology and its development trend are introduced.

1.1 General Development of BTS Antenna Technology

In the cellular mobile communication system, antenna is the transducer between the

signals of communication equipment circuit and air radiated electromagnetic wave; in

other words, antennas convert electromagnetic waves into electrical currents and vice

versa. It is the connector in wireless air communication.

Cellular communication system requires reliable communications between BTS and

MS, it has specific requirements on antenna system. The radio signal power sent out

from the transmitter will be delivered to antenna through antenna feed (cable), then it

will be sent out in the form of electromagnetic wave. When the electromagnetic wave

arrives at the receiving site, it is received by the antenna at the site (just a fraction of

the power is received), then it is delivered to the radio receiver through antenna feed. It

is obvious that antenna plays a very important role in sending and receiving

electromagnetic wave. Telecommunication won’t be possible without antenna’s

participation. Telecommunication performance is largely affected by antenna

gain 、 antenna coverage direction 、 beam width 、 usable driving power 、 antenna

configuration and its polarization mode, etc..

Technology & market status of Chinese antenna suppliers

As shown in some related materials, in the fields of high-tech commercial BTS

antenna 、 smart antenna and Bluetooth antenna, which are used in mobile

communications、spread spectrum communications and microwave communications,

Chinese antenna suppliers only take 20% market share of the whole; and compared

with the famous foreign suppliers, their production scale and strength are far left

behind. Generally speaking, Chinese antenna suppliers feature in large amount、small

scale and weak strength. According to incomplete statistical survey, until the first half

year of 2002 there were more than 100 manufacturers providing communication


1


antennas, and most of them were medium/small-sized. In terms of annual production

and sales volume, only a few of them have reached above 30 millions (RMB) with

more than 200 employees, which included Xi'an Haitian Antenna Technologies Co.,

Ltd., MOBI Antenna Technologies (SHENZHEN) co., Ltd., Kenbotong

Communication Ltd., Guangdong Shenglu Telecommunication Tech Co.,Ltd., and

Tongyu Communication Equipment Co., Ltd., etc..

Advantages of foreign antenna manufacturers

Most of foreign antenna manufacturers possess solid financial strength 、 high brand

fame and abundant talents and technologies. Several among them have a history of

over half a century, and world famous brands, with which their annual sales volumes

exceed USD 2 billions; while the annual sales volume of the largest Chinese domestic

antenna manufacturer is just over RMB 100 millions, which is just a small fraction of

that of the foreign giants. What’s more, after China entered WTO, famous foreign

antenna manufacturers, leading Allen Telecom Inc., Andrew company and Katherine

company, have started to invest in building factories in China, which has made a great

impact on China’s national antenna manufacturers.

Development trend of antenna industry

In 1897, Marconi created antenna and for the first time realized radio communication.

The history of antenna is just about a century, but because of its important application

in military, it has been highly valued and emphasized. Due to the development in the

past half century, the hardware technology of antenna is now relatively mature. Now

antenna design is developing towards wide band、multi-function and high density of

integration. Various kinds of antenna technologies like dual-polarization 、adjustable

electrical down-tilt and multi-frequency band multiplexing are gradually being

launched into commercial operation; great advances have been made in smart antenna

technology too.

After twenty years development, the technology gap between homemade antennas and

the famous foreign brands is being narrowed; some skills used in homemade antennas

are even equally matched with the advanced foreign skills. In China, the brand fame

and credit worthiness have been increased gradually. While the gaps in capital and

talents are still wide. Homemade antennas feature in moderate prices, good services,

and fulfilling the needs of communication construction.


2


1.2 Theories of Antenna Radiation

Antennas must be able to efficiently convert the circuit signals in the BTS equipment to

electromagnetic waves in the free airspace and vice versa. The efficiency and ability of

antenna electromagnetic radiation is a very professional microwave technology. Here

introduced are some radiation theories of antenna element, which are most frequently

used currently.

1.2.1 Electromagnetic Wave Radiation of Electric Dipole

The conductor whose length is much shorter than the wavelength is referred to electric

doublet. When there is alternating current running in the wire, electromagnetic wave

radiation may happen, the power of which is affected by the length and shape of the

wire. As shown in Picture 1-1: if two wires are too close to each other, electromagnetic

wave will be limited inbetween them, and its power is very weak; if the two wires are

stretched to a certain angle, the Electromagnetic field will spread in the space around,

and the radiation power will increase.

We must note that when the wire length( L) is far shorter than the wave length (λ), the

radiation power is very weak; when wire length is increased to more or less the wave

length, the alternating current in the wire will strengthen accordingly, thus the radiation

will be more powerful.

Picture 1-1 Diagram of Relation between Doublet Angle and Radiation Power of

Electromagnetic Wave

1.2.2 Half-wave Dipole

Half-wave dipole is the most widely used type of antenna so far. A single half-wave

doublet can function independently or be used as paraboloid antenna feed; several half-

wave doublets can be adopted to form an antenna array.


3


Dipole with two arms of the same length is called balanced dipole. When the length of

each arm is 1/4 wave length, and full length of two arms is 1/2 wave length, the dipole

is referred to half-wave doublet. See picture 1-2.

Picture 1-2 Half-wave Dipole

There is another kind of half-wave dipole, which can be obtained by forming a full-

wave doublet into a slender rectangular with the two ends of the doublet overlapped.

The slender rectangular is called folded dipole, the length of which is also 1/2 wave

length, so it is also referred as half-wave folded dipole.

Picture 1-3 Half-wave Folded Dipole

1.3 Internal Structure & Types of Mobile Communication BTS Antenna

1.3.1 Plate-shaped Directional Antenna

Directional plate-shaped antenna is the most widely used BTS antenna and is of great

importance. This kind of antenna features in high gain、good sector directional pattern、This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements.

4


small back beam 、 reliable sealability, convenient control over depression angle of

vertical pattern、and long performance life.

See Picture 1-4 for antenna appearing.


5


Picture 1-4 Diagram of Directional Plate-shaped Antenna Appearing

1.3.1.1 Formation of High Gain

Picture 1-5 Vertically-set Line Array Formed by Several Half-wave Dipole


6


Picture 1-6 Apply horizontally oriented theory by adding baffle-board to one side

the line array (take the line array of double half-wave dipole with baffle-board

as an example )

Currently, almost all antenna manufacturers adopt plate-shaped dipole array structure

in designing BTS directional antennas. Two types of dipole are adopted.

1.3.1.2 Balanced Dipole

It is standard half-wave balanced dipole (add one additional dipole to lower the

dipole’s ground clearance, and reduce the thickness of antenna).


7


Picture 1-7 Directional plate-shaped antenna formed with several half-wave dipole

1.3.1.3 Microstrip Dipole

It is a variant of half-wave dipole. It uses transmission line of 1/4 wave length to form

radiation.


8


Picture 1-8 Directional plate-shaped antenna consisting of several microstrip

dipole

1.3.1.4 Dipole Array Structure of BTS Antenna

Picture 1-9 Structure of plate-shaped directional antenna array

1.3.2 Isotropic Dipole Antenna with Series Feed

Isotropic antenna adopts several half-wave dipoles with series feed to create and

increase radiation gain.


9


Picture 1-10 Structure of Isotropic Dipole Antenna with Series Feed


10


2 Concepts & Meanings of Antenna Parameters

Knowledge point

This chapter mainly introduces the concepts of BTS antenna technology parameters

and their significant application in network planning.

2.1 Antenna Gain

Gain as a parameter measures the directionality of a given antenna. The gain of an

antenna is a passive phenomenon - power is not added by the antenna, but simply

redistributed to provide more radiated power in a certain direction than would be

transmitted by an isotropic antenna. If an antenna has a greater than one gain in some

directions, it must have a less than one gain in other directions since energy is

conserved by the antenna. Sometimes, the half-wave dipole is taken as a reference

instead of the isotropic radiator. The gain is then given in dBd (decibels over dipole).

Antenna gain is usually expressed in dBd or dBi. dBi represents a reference value( of

the antenna field strength in the direction with highest radiation power) relative to

isotropic radiator (see Picture 2-11); antenna gain of half-wave dipole is expressed in

dBd. There is a fixed difference between the two (see Picture 2-11), that is 0dBd equals

to 2.15dBi.

Picture 2-11 Diagram of antenna gain in dBi and dBd

Currently, antennas with gains ranging from 0dBi to 20dBi are used in both domestic

and foreign BTSs. Gain of antenna used for indoor micro cellular coverage usually

本文中的所有信息均为中兴通讯股份有限公司内部信息，不得向外传播 11


ranges from 0 to 8 dBi; that of antenna on outdoor BTS is from 9dBi (isotropic

antenna gain) to 18dBi (directional antenna gain).

Antennas with around 20dBi gain and relatively narrow beam width are usually used in

the coverage on the vast but less populated highways.

2.2 Directional Diagram of Radiation

Directional diagram of BTS antenna radiation falls into two types: isotropic radiation

diagram and directional radiation diagram. As shown in Picture 2-2, the two on the left

of the diagram are the horizontal sectional drawing and solid radiation drawing of

isotropic antenna; on the right are the horizontal sectional drawing and solid radiation

drawing of directional antenna. The radiation strength of isotropic antenna in all

directions of the same horizontal plane is theoretically the same. It applies to isotropic

cells. The red part in Picture 2-2 is the metal baffle-board in the radome of directional

antenna, which enables the antenna to radiate into different directions on the horizontal

plane. It applies to cover fan-shaped cells.

Picture 2-12 Field strength diagram of isotropic antenna and directional antenna

2.3 Beam Width

2.3.1 Horizontal Beam Width

The horizontal beam width of isotropic antenna is 360 (see the right one in Picture 2-

3), while the common horizontal beam width (3dB) of directional antenna includes:

20、30、65、90、105、120、180 (see the left one in Picture 2-3).



Picture 2-13 Diagram of horizontal beam width (3dB) of BTS antenna

The gain of antenna with 20or 30 horizontal beam width is higher, which is usually

used in covering strip areas and highways; antenna with 65 beam width is used in the

coverage for the typical three-sector sites in dense urban area; antenna with 90 beam

width is used in the coverage of the three-sector of typical site in suburb area; antenna

with 105 beam width is used in the coverage of the three-sector of typical site in the

vast and less populated area. See Picture 2-14.

Antenna with 120、180beam width is used to cover the special-shaped sectors with

extremely wide angles.


13


Picture 2-14 Diagram of BTS antenna coverage

2.3.2 Vertical Beam Width

Picture 2-15 Diagram of BTS antenna vertical with 3dB beam width

The 3dB vertical beam width is closely related to the antenna gain and the 3dB

horizontal beam width. The 3dB vertical beam width is about 10. Generally, in the

antenna with same gain and same antenna designing skills, the wider the horizontal

beam width is, the narrower the vertical beam width will be.

The narrower 3dB vertical beam width will create larger shade area, as shown in

Picture 2-15. Of the two sets of antennas with the same height and without down-tilt,

the shadow area created by the wider vertical beam width is OX’’ (red area), which is

smaller than that created by the narrower vertical beam width OX (blue area).

When selecting antenna types, with the same antenna gain, we’d better select

those with wider 3dB vertical beam width, so as to ensure the coverage of the

serving area and reduce shadow area.


14


2.4 Frequency Band

For different BTSs, the frequency band of antenna selected should include those

required.

For GSM900 system, double-frequency antennas for 890-960MHz、870-960MHz、807-

960 MHz and 890-1880 MHz are all applicable.

For CDMA800 system，use 824－896MHZ antenna.

For CDMA1900 system, use 1850－1990MHZ antenna.

In order to reduce the out-of-band interference signal, band width of the selected

antenna may just satisfy the frequency band’s requirement.

2.5 Polarization Mode

BTS antenna usually adopts linear polarization mode, as shown in Picture 2-16. Uni-

polarization antenna often adopts vertical linear polarization; dual-polarized antenna

often adopts 45bilinear polarization. As one dual-polarization antenna is made up of

two orthogonal antennas in one radome (Picture 2-17), the adoption of dual-

polarization antenna can help reduce number of antennas, simplify installation

procedures, reduce cost and occupied space.


15


Picture 2-16 Common polarization mode of BTS antenna

Picture 2-17 Diagram of dual-polarization BTS antenna

2.6 Down-tilt Mode

In order to expand the coverage on areas nearby the BTS, and reduce shadow area and

interference to the adjacent BTSs, antenna shall not be installed too high, and in the

mean time down-tilt mode shall be adopted. As shown in Picture 2-18, the shadow

areas created by the lower antenna (yellow) and the down-tilt antenna (green) are OX’’

and OX’, which are both smaller than that created by the high antenna (blue) without

down-tilt OX.


16


Picture 2-18 Diagram of BTS antenna down-tilt

There are several modes of antenna down-tilt: mechanical down-tilt, settled electrical

down-tilt, adjustable electrical down-tilt, remote-adjustable electrical down-tilt. As for

mechanical, it is just set slant during installation; it is often used in antenna with down-

tilt angle within 10. When the down-tilt is further expanded, the right ahead of the

coverage will appear sunken, and the two edges appear squashed, the directional

diagram becomes deformed, and in the mean time interference to the adjacent BTSs

becomes stronger, as shown in Picture 2-19. Another defect of mechanical down-tilt is

that the back lobe of antenna will upward, which can result in interference to the

adjacent sectors and call drop to MS on upper layer of adjacent cells.

Picture 2-19 Comparison on BTS antenna down-tilt modes

The angle of electrical down-tilt antenna is relatively wide (can be wider than 10); the

directional diagram is not apparently out of shape; the back lobe declines in the mean

time; there is no interference to MS on adjacent high buildings.


17


2.7 Antenna Front-to-back Ratio

The indicator of antenna front-to-back ratio is related to the electric dimension of

antenna baffle-board. Larger electric dimension can provide better front-to-back ratio

index. For example, the horizontal dimension of antenna with horizontal 3dB beam

width and 65angle is larger than that of antenna with horizontal 3dB beam width and

90 angle, thus the former one excels the later one. The front-to-back ratio of outdoor

BTS antenna should be larger than 25dB. Since micro cellular antenna is relatively

smaller in dimension, its front-to-back ratio index should be smaller than 25dB.

2.8 Antenna Input Impedance( Zin)

Definition: antenna input impedance is the ratio of input-end signal voltage to the

signal current. It consists of resistive component (Rin) and reactive component (Xin),

Zin= Rin + j Xin. The existence of Xin will reduce the signal power that antenna

extracts from the feed, so we shall make Xin=0 as possible, that is we shall make

antenna input impedance a pure resistance. As a matter of fact, even if it is a well-

designed and well-modulated antenna, its input impedance still consists of Xin of small

value.

Input impedance is related to the structure、dimension and operating wavelength of the

antenna. Half-wave dipole is the most important basic antenna, its input impedance is

Zin = 73.1＋ｊ 42.5 (Ω). When its wavelength is shortened by （３～５）％, the Xin

in it can be eliminated, and the antenna input impedance can be pure resistance; its

input impedance now is Zin = 73.1(Ω), (characteristic impedance 73.1Ω). Precisely

speaking, antenna input impedance of pure resistance is only considered in terms of dot

frequency.

The input impedance of half-wave folded dipole is four times that of half-wave dipole,

that is Zin = 280 (Ω) (characteristic impedance 300Ω).

However, within the required operating frequency range, through modulation of

antenna impedance, we can make the imaginary part of the input impedance very small

and real part very close to 50Ω, thus the antenna input impedance can be Zin = Rin =

50Ω, which is a must for good impedance match between antenna and the feed.


18


2.9 Antenna VSWR

Antenna VSWR is the indicator for matching degree between antenna feed and BTS.

Definition of VSWR:

Umax——the anti-node voltage on feeder

Umin——the wave node voltage on feeder

Because the input wave can not be absorbed completely when it’s delivered to the

input end B of antenna, and reflection wave occurs and overlays, VSWR will form.

The larger VSWR is, the larger the reflection will be, and the worse the matching will

be.

What bad effects can be resulted from bad VSWR? What is the acceptable VSWR? An

appropriate VSWR shall be the balance between the quantity of energy lost and the

generating cost.

(1) VSWR＞1, it means that some of the power input into the antenna is reflected,

and the radiation power is reduced；

(2) The feed loss is increased. Loss rate of 7/8＂cable is 4dB/100m, which is the result

based on the condition of VSWR=1 (perfectly-matched); energy loss is increased

due to the reflection of power, thus the input power from feed to antenna is

reduced.

2.10Side Lobe Suppression & Null Fill

As antennas are usually installed on high places of metal towers or buildings, side

lobes on vertical plane (especially the first side lobe) shall be suppressed as much

as possible, so as to reduce energy loss. In the mean time, the compensation to the

downward side lobe null on vertical plane shall be strengthened to make the null

depth of the sector pattern shallow, so as to improve the coverage of adjacent area

of BTS and reduce shadow area and blind spots. Picture 2-20 shows the contrast

between BTS antenna with null fill and that without null fill, the horizontal


19


ordinate showing the distance to the BTS, the vertical ordinate showing the

ground signal strength.

Picture 2-20 Diagram of comparison between BTS antenna with or without null fill effect

Null fill = (vertical first lower null fill value/ radiation direction maximum)%

= 20log (vertical first lower null fill value/ radiation direction maximum)dB

Strictly speaking, antennas without features of side lobe suppression and null fill shall

not be used, so as to ensure good coverage over the serving area.

2.11 Third-order Intermodulation

The third-order intermodulation indicator of most foreign antennas can reach -

150dBC@243dBm, while that of the common antennas is just -130 d B C@2 43d B m

. The difference is related to the design of antenna and the selection of connector.

Because the strength of received signal is much weaker than that of transmission signal

at BTS, once the intermodulation product of transmission signal of multi-carrier falls

into the receiving frequency band, the BTS will not be able to function normally.


20

mailto:-130dBC@2(43dBm


2.12Isolation between Ports

When multiport antenna is used, the isolation between ports shall be more than 30dB.

For example, isolation between the two different polarized ports of dual-polarization

antenna, isolation between the two ports with different frequency bands of outdoor

double-frequency antenna, isolation among the four ports of double-frequency and

dual-polarization antenna, all should be more than 30dB.

2.13Case


21

内部公开▲

3 Measurement of Key Antenna Indicators Knowledge point

This chapter mainly introduces the measurement method, measurement theory and

measurement environment of key indicators of BTS antenna.

3.1 Measurement of Antenna Gain

(1) Choose standard plain antenna measurement field. Indstall antenna and connect

instruments and meters according to Picture 3-21;

Picture 3-21 Block diagram of measurement of antenna gain、half-power beam

width、front-to-back ratio、cross polarization discrimination

(2) Direct datum gain antenna to the direction of central lobe of the source antenna,

then take down the receiving level of datum gain antenna P1(dBm);

(3) Direct the measured antenna to the direction of central lobe of the source antenna,

take down the receiving level of datum gain antenna P2(dBm);

(4) Calculate and get the gain of the measured antenna: G=（gain of datum antenna

G0）+(P2－P1);

(5) In order to show the gain feature of antenna in the given frequency band, at least

measure three frequency points in high /medium/low frequency band.

3.2 Measurement of 3dB Beam Width & Front-to-back Ratio

(1) Choose standard plain antenna measurement field. Install antenna and connect


内部公开▲

instruments and meters according to Picture 3-21;

(2) Direct the measured antenna to the direction of central lobe of the source antenna,

then start the rotating floor to make the measured antenna rotate horizontally, and take

down the receiving level of the measured antenna according to the function of angles of

rotation, then from the function curve get the half-wave beam width and front-to-back

ratio of the measured antenna;

(3) Keep the measured antenna aflat with its top pointing at the direction of central

lobe of source antenna, then start the rotating floor to make the measured antenna

rotate horizontally, and take down the receiving level of the measured antenna

according to the function of angles of rotation, then get the vertical half-wave beam

width of the measured antenna from the function curve;

(4) In order to show the gain feature of antenna in the given frequency band, at least

measure three frequency points in high /medium/low frequency band.

3.3 Measurement of Antenna VSWR

(1) Choose standard plain antenna measurement field or chamber without echo to

install antenna according to Picture 3-22;

Picture 3-22 Block diagram of VSWR measurement

(2) At the calibration port, fine-tune the meters and instruments with a short circuit

device or a open circuit instead of the measured antenna;

(3) Connect the calibration port with the measured antenna, read the VSWR of the

measured antenna.


23

内部公开▲

3.4 Isolation Measurement of Dual-Polarized Antenna



Picture 3-23 Block diagram of antenna isolation

(2) Short-circuit the two feeds to the measured dual-polarized antenna, reset the

meters to 0dB;

(3) Connect the meter feeds with the measured antenna, read the worst isolation of the

measured dual-polarized antenna.

3.5 Measurement of Intermodulation



Picture 3-24 Block diagram of antenna intermodulation measurement

(2) In the operating frequency band, choose two appropriate frequencies f1h and f2h ,


24

内部公开▲

make the intermodulation product f3=2f2-f1 (or f3=2f1-f2), which is also required to

be within the operating frequency band;

(3) F1 and f2 input 20W individual tone power to the antenna simultaneously;

(4) With f3 receiver, read the level of three-order intermodulation product.


25

内部公开▲

4 Antenna Parameters

Knowledge point

This chapter mainly introduces the engineering parameters of antenna in network

planning and their influences on coverage, and how to improve network performance

with changes in engineering parameters.

4.1 Antenna Directional Angle

The electromagnetic field of antenna radiation distributes in compliance with the

angular coordinates in a fixed distance, the graph of which is called directional diagram

(directional pattern). The diagram expressed with field strength is called field strength

pattern. The diagram expressed with power density is called power pattern. The

diagram expressed with phase is called phase pattern.

Antenna directional diagram is a solid figure in space, but it is usually expressed with

the pattern formed with two orthogonal principal planes, which is called plane pattern (

or vertical pattern or horizontal pattern). As for horizontal pattern, it is classified into

isotropic antenna pattern and directional antenna pattern. Directional antenna pattern

consists of many shapes, such as heart-shaped and 8-shaped, etc..

Antenna has directional property due to oscillator array and changes in oscillator feed

phase, which is theoretically similar to optical interference effect. Therefore, energy in

some directions is increased, while in other directions is reduced, that is how antenna

lobes (beams) and null come into being. The lobe with strongest energy is called

principal lobe; the upper/lower lobe with second strongest engergy is called first side

lobe; make analogy like this. As for directional antenna, it has back lobe except for

those lobes above.

Adjustment of antenna directional angles is of great importance to the performance of

mobile communication network. On one hand, precise directional angles can ensure the

real BTS coverage meeting our expectations and thus ensure the operation quality of

the whole network; on the other hand, adjustment of directional angles according to

call traffic volume and actual network conditions can further optimize the existing

networks.


内部公开▲

Based on ideal cellular communication model, directional BTS is usually divided into

three cells in the current GSM system (mainly with ERICSSON equipment):

Cell A: azimuth angle 0°, antenna pointing to due north;

Cell B: azimuth angle 120°, antenna pointing to southeast;

Cell C: azimuth angle 240, antenna pointing to southwest.

In GSM network construction and planning, we install and adjust antenna azimuth

angle strictly according to the rules above, which is one of the installation

specifications. Deviation in the setting of azimuth angle can result in unreasonable

discrepancy between the real coverage and the designed coverage and some

unexpected co-channel or adjacent channel interference.

In the real GSM network, specific landforms like high buildings 、mountains and water

face, etc. can cause signal refraction and reflection, which can result in big discrepancy

between the real coverage and the ideal model, thus some areas enjoy stronger signals,

while some suffer from weaker ones. In this case, we shall appropriately adjust the

antenna azimuth angle according to the real network situation, so as to ensure the

signal strength in the weak areas and achieve the goal of network optimization.

Besides, the discrepancy in real population density of different areas can cause call

traffic unbalance in cells under the antennas’ coverage. Again we can adjust the

antenna azimuth angle to make traffic balanced. Certainly, we usually don’t

recommend adjustment in antenna azimuth angle, because interference in system may

be resulted to some degree. While in some special circumstances, like some emergent

meetings or large-scale public activities, the traffic concentrates in come cells, we can

make adjustment in antenna azimuth angle for the occasion, in order to balance the

traffic and optimize the network. What’s more, as for the signal blind zone or weak

zone in suburb, we can also achieve network optimization through adjustment in

antenna azimuth angle; but remember to test the signal in around area with field

strength test vehicles, so as to ensure the network operation quality.

4.2 Antenna Height

The signal power received at the receiver is related to many factors, which can be

concluded into two types:


27

内部公开▲

Parameters at the transmitting terminal and the receiving terminal;

Interference from landforms and ground objects.

Parameters at transmitting and receiving terminals include: transmitting

power、antenna gain、feed loss、antenna height、operating frequency, and the distance

between transmitting terminal and receiving terminal. Interference from landforms and

ground objects is caused by landform fluctuations and ground objects’ screening of

signals. All transmission models are related to the height of antennas, therefore antenna

height has great influence on path loss.

The coverage distance between transmitting terminal and receiving terminal can

approximately be expressed with the following formula:

receiving power

transmitting power

height of receiving antenna

height of transmitting antenna

gain of receiving antenna

gain of transmitting antenna

path-loss improvement factor

When parameters at transmitter and receiver are fixed, the coverage distance is in direct

proportion to the height and gain of antenna.

Due to fewer base stations at the beginning period of GSM network construction, BTS

antennas were usually installed relatively higher. As mobile communication has

developed swiftly in recent years, number of BTS has increased dramatically; there is a

site every 500m in urban areas. In this case, we must reduce the BTS original coverage

and lower antenna height, or network quality will be severely influenced. Main related

influences fall into three aspects as shown bellow:

(1) Unbalanced traffic. Over high antenna will result in over large BTS coverage and

too much traffic in one BTS. While the traffic in adjacent BTS is less due to its small


28

内部公开▲

coverage and being covered by the BTS with too large coverage, thus it can not

function well and unbalanced traffic will be caused.

(2) Interference within system. Over high antenna can cause cross-BTS interference

(mainly including co-channel interference and adjacent channel interference) 、 call

drop 、 cross talk and too much stray noise, thus the quality of the whole radio

communication network will decrease.

(3) Island effect. It is about BTS coverage problem. When the BTS is covering

special landforms like vast water face or mountainous areas, though the original

coverage distance remains the same, an “exclave area” will appear in the far distance,

because of the reflection from water face or mountains; while the adjacent BTSs

having handover relation with the BTS can not be covered due to obstruction of the

landforms. Therefore, handover relation between the “exclave area” and the adjacent

BTSs does not exist, and the “exclave area” becomes an island. When a MS uses the

signal in the “exclave area”, it can easily suffer from call drop due to lack of handover

relation.

4.3 Antenna Down-tilt

Make the principal lobe of antenna lean in a certain angle through antenna down-tilt, to

reduce the power level to the adjacent BTS, which is to reduce interference.

As a matter of fact, the value of antenna down-tilt is directly related to the parameters

of antenna height 、coverage semi-diameter 、vertical beam and electrical down-tilt.

When the coverage semi-diameter is fixed, the higher the antenna is, the larger down-

tilt is needed; if the antenna height is fixed, the smaller the coverage semi-diameter is,

the larger the down-tilt should be.

In urban area where the scattering of BTSs is dense, it’s quite easy that interference

between BTSs occur. In order to make most of the energy be radiated within the

coverage and reduce interference from adjacent cells, when setting the initial down-tilt,

we should make the half-power points on the principal lobe aim at the coverage rim.

The calculation formula is as follows:

α= arctg(2H/L)×（180/π）+（β/2）–γe


29

内部公开▲

In areas like suburb、villages、highways and sea face, in order to get coverage as far as

possible, we can narrow the down-tilt, and make the maximum gain point aim at the

coverage rim. The formula of down-tilt is shown bellow:

α= arctg(H/L) ×（180/π）+（β/2）–γe

In the above formulas,

α is the initial mechanical tilt of the antenna, expressed in degree;

H represents the effective height of the BTS, which is the difference between the fixed

location of antenna and the average height of the area covered, expressed in meter;

L represents the distance from the BTS antenna to the sector’s rim needed to be

covered, expressed in meter;

β represents vertical beam width of the antenna, expressed in degree;

γe represents down-tilt of the antenna, expressed in degree.


30

内部公开▲

5 Antenna Types

Knowledge point

In this chapter, we’ll get to know the classification methods of antenna, the basic

classification of BTS antenna; and through examples of typical antennas, get to know

the value range of antenna and the exterior appearance of different types of antennas.

5.1 Antenna Types

There are various kinds of antennas, so as to meet requirements of different

frequencies、different applications、different situations. For so many kinds of antennas,

there are a variety of classification methods:

Classification by use: communication antenna, TV antenna, radar antenna, etc.;

Classification by operation frequency band: short wave antenna, ultra-short wave

antenna, microwave antenna, etc. ;

Classification by appearance: line-shaped antenna, plane-shaped antenna, etc. ;

Classification by directivity: isotropic antenna, directional antenna, etc..

Since there is no big difference in operating frequency、antenna gain and front-to-back

ratio of different antennas used in mobile communication systems, we’ll analyze and

compare them in terms of down-tilt’s influence on antenna pattern and radio network.

Isotropic antenna

Isotropic antenna radiates in all directions (360°) of the horizontal pattern, which

means it radiates without particular directivity. As for the beam with fixed width on

vertical pattern, normally the smaller the beam width is, the higher the antenna gain

will be. This kind of antenna is often used in BTS at suburb with large-cell model,

since it features in larger coverage.

Directional antenna

Directional antenna radiates within some certain angle, which means it radiates with

particular directivity. As for the beam with fixed width on vertical pattern, normally the

smaller the beam width is, the higher the antenna gain will be. This kind of antenna is

often used in BTS at urban area with small-cell model, since it features in smaller

coverage, denser subscriber intensity and higher frequency utility ratio.


内部公开▲

We set up different types of BTSs according to requirements of network construction;

and different types of BTSs use different types of antennas according to their needs.

The basis for using different antennas is the technical parameters mentioned above.

Isotropic BTS adopts isotropic antenna with same antenna gain in all horizontal

directions; and directional BTS adopts directional antenna with changing antenna gain

in a particular horizontal direction. Usually antenna with horizontal beam width B=65°

is used in urban area; and antenna with horizontal beam width B=65°、90° or 120° is

often used in suburb (based on the BTS type and the local landforms); while in

villages, the application of isotropic antenna with large coverage is the most economic.

Mechanically-adjustable antenna

The so called mechanically-adjustable antenna is a kind of antenna whose down-tilt can

be adjusted mechanically.

After mechanically-adjustable antenna is vertically installed, position of the bracket at

the back of it can be adjusted, if there is need in network optimization. During the

adjustment of bracket, there is obvious change in the coverage distance of the principal

lobe, but the amplitudes of vertical component and horizontal component remain the

same, thus the antenna pattern is easy to be out of shape. Practice has proved that the

best down-tilt range is 1°－5°. When the down-tilt changes from 5° to 10°, the antenna

pattern deforms a little bit. When it changes from 10° to 15°, the antenna pattern

deforms to a larger extent. When it is larger than 15°, there is big change on the

antenna pattern, which changes from a pear-shaped one to a spindle-shaped one; now

the coverage distance of principal lobe is obviously shortened, but not all parts of the

antenna pattern are within the BTS sector, which means that signal from this BTS can

be received in the adjacent BTS sector, thus serious interference in the system will be

caused.

Besides, if it’s needed to adjust the down-tilt of this kind of antenna in the daily

maintenance, the whole system shall be shut down. We can not keep monitoring

network indicators while adjusting the down-tilt. It is very troublesome to adjust the

down-tilt, because it needs maintenance staff to climb to where the antenna is located.

The down-tilt angle is a theoretical value obtained from the calculation of computer

analog analysis software, which is a little deviated from the actual best down-tilt. The

stepping degree for adjusting down-tilt is 1°, and the third-order intermodulation

indicator is -120dBc.

Electrical antenna


内部公开▲

The so called electrical antenna is a kind of antenna, which features in electrical down-

tilt.

The theory of electrical down-tilt is to change the amplitudes of vertical component

and horizontal component and the field strength of compound component, so as to

make vertical pattern of the antenna decline. Because the antenna field strength

increases and decreases at the same time in different directions, the antenna pattern

won’t change too much after down-tilt adjustment, the coverage distance of principal

lobe will be reduced, and in the mean time the antenna pattern will reduce its coverage

over the serving sector without producing any interference. Practice has proved that

when the down-tilt of electrical antenna changes from 1° to 5°, the antenna pattern is

roughly the same as that of mechanically-adjustable antenna. When the down-tilt

changes from 5° to 10°, the antenna pattern is improved a little compared with that of

mechanically-adjustable antenna. When down-tilt changes within 10° and 15°, the

antenna pattern changes greatly. When the down-tilt is larger than 15°, the antenna

pattern is obviously different from that of mechanically-adjustable antenna, its shape

isn’t changed much, but the coverage distance of principal lobe is obviously reduced,

and the whole antenna pattern is within the BTS sector; we can increase down-tilt to

reduce the sector coverage without any interference. This is the expected ideal antenna

pattern. It’s proved that adoption of electrical antenna can reduce call loss and

interference.

What’s more, electrical antenna allows down-tilt adjustment without shutting down the

system, which keeps the monitoring on adjustment effects. The stepping precision is

relatively higher (0.1°), thus we can make fine adjustment on the network. The third-

order intermodulation indicator for electrical antenna is -150dBc; there is a difference

of 30dBc compared with that of mechanically-adjustable antenna. This is in favor of

eliminating adjacent-channel interference and stray interference.

Dual-polarized antenna

Dual-polarized antenna uses new technology. It combines two sets of antennas with

mutually orthogonal polarization directions (+45° and -45°) and works in the duplex

model of transmitting and receiving signals in the mean time. Therefore, its outstanding

advantage is that it saves antennas for directional BTS. Normally the directional BTS

(three-sector) of GSM digital mobile communication network needs to use 9 antennas;

each of its sectors uses 3 (for space diversity, one for transmitting, two for receiving


33

内部公开▲

signals). If dual-polarized antenna is adopted, each sector needs only one antenna. In

the mean time, the orthogonality of ±45° polarization can ensure that the isolation

between the two sets of antennas (+45° and -45°) meets the requirement from

intermodulation （ ≥ 30dB ） , therefore the space interval between dual-polarized

antenna is just 20-30cm. Besides, dual-polarized antenna also possesses advantages

like reducing call loss and interference and improving the whole network quality,

which are the same as those of electrical antenna. What’s more, there is no specific

requirement for installing dual-polarized antenna and no need to acquire land for

building antenna tower. What’s needed is just a metal pole with 20cm diameter, and

then fix the antenna on the pole in the corresponding coverage direction. In this way,

basic construction cost is saved, and layout of BTS is more reasonable, and it’s much

easier to selection BTS location.

As for the selection of antenna type, we should select the antenna which meets the

needs of the local mobile network according to specific situations like network

coverage, call traffic volume, interference and network service quality.

--- in dense BTS area with high traffic volume, use dual-polarized antenna and

electrical antenna;

--- in suburb area with fewer BTS and low traffic, where larger coverage is required,

use the traditional mechanically-adjustable antenna.

Currently in area with dense traffic, the network call loss is high and interference is

big. One important reason is that the down-tilt of mechanically-adjustable antenna is

too large, which causes serious deformation of antenna pattern. In order to solve the

off-capacity problem we must shorten the distance between BTSs and enlarge down-

tilt. While if mechanically-adjustable antenna is used, antenna pattern starts to deform

when the down-tilt is larger than 5°; when it’s larger than 10°, antenna pattern will be

seriously out of shape. Therefore, the problems can not be solved by using

mechanically-adjustable antenna. It is recommended to use electrical antenna or dual-

polarized antenna instead of mechanically-adjustable antenna in dense traffic area. The

replaced mechanically-adjustable antennas can be used in areas with less traffic, like

villages and suburb.


34

内部公开▲

6 Circumstances of Antenna Application

Knowledge point

In this chapter, several real scene pictures are shown to illustrate antenna coverage

area classification and related radio environment.


35

内部公开▲

6.1 Dense Urban

Picture 6-25 Dense urban

6.2 Urban (Towns)


36

内部公开▲

Picture 6-26 Urban (towns)

6.3 Suburb (Counties) & Villages

Picture 6-27 Suburb

6.4 Railways/ Highways (Roads)


37

内部公开▲

Picture 6-28 Railways & highways

6.5 Scenery Areas

Picture 6-29 Scenery areas


38

内部公开▲

7 Selection of Antenna Type

Knowledge point

Combining with the real scene pictures, this chapter introduces classification of

coverage area and the selection of corresponding antenna.

7.1 BTS antenna selection for urban

Application environment feature: In urban area BTSs are densely distributed. The

coverage of a single BTS shall be small in order to avoid overshooting and reduce

inter-BTS interference. And in the mean time increase frequency multiplexing

Principles for antenna selection:

(1) Selection of polarization model: because it’s difficult to obtain BTS location in

urban area and there is space limit for antenna installation, it is recommended to use

dual-polarized antenna;

(2) Selection of antenna pattern: improving frequency multiplexing shall be mainly

considered in urban area, so directional antenna is the best option;

(3) Selection of half-power beam width: in order to better control the cell coverage

and suppress interference, half-power beam width shall be within 60~65°;

(4) Selection of antenna gain: since large coverage is not needed in urban area, it is

recommended to use antenna with medium gain (15-18dBi). The microcells used for

filling blind zones can use antennas with lower gain;

(5) Selection of down-tilt: in urban area, antenna tilt needs to be adjusted frequently,

and some antenna tilts are required to be set larger. Since mechanically-adjustable

antenna is good for controlling interference, it is suggested that antenna with preset

down-tilt be adopted. Therefore, antenna with fixed electrical down-tilt is

recommended; or electrical antenna when related conditions are satisfied.

7.2 BTS antenna selection for suburb

Application environment feature: in suburb or villages, BTSs are sparsely distributed

and call traffic volume is small, thus large coverage is requested. There is only one


内部公开▲

BTS in some places and large coverage is of great importance. In this case, we need to

take into consideration around areas of the BTS which need to be covered, when we

make antenna selection.


(1) Selection of antenna pattern: if the BTS is required to cover the around area

without particular directivity, and call traffic is scattered, it is suggested that isotropic

antenna be used. We should note that coverage of isotropic antenna is not as far as that

of directional antenna due to its smaller antenna gain; and pay attention to the tower

body’s influence on coverage; and the antenna shall be kept vertical to ground. If

farther coverage distance is required by customers, then directional antenna shall be

adopted; normally, horizontal half-power directional antennas with beam width of 90 °,

105 °, 120 ° are recommended;

(2) Selection of antenna gain: based on coverage requirement, it is recommended to

adopt directional antenna with higher gain （ 16-18dBi ） or isotropic antenna with

gain of 9－11dBi in suburb area or villages;

(3) Selection of down-tilt: adjustment on antenna down-tilt is seldom needed in

suburb area, and requirement on adjustment range is not high, it is suggested that

mechanically-adjustable antenna be used; meanwhile, if antenna height is above 50

meters and there is request for coverage of proximal area, we can use antenna with

null-fill antenna to avoid blind zone under the tower.

7.3 BTS antenna selection for highway coverage

Application environment feature: on highways, call traffic volume is low and

subscribers move fast, so coverage is the key issue. Usually, the antenna needs to

provide zonary coverage, so directional antenna is recommended to be used. Isotropic

antenna can be adopted where the highway passes through towns or scenery areas. Vast

coverage is also requested, so we need to select antenna type based on BTS location and

BTS type. Conditions of highways can be quite different. There are plain and straight

ones, like express highway, railway, national highway and provincial highway, etc.. It is

recommended to set up BTSs at the side of highway and adopt S1/1/1 or S1/1 BTS type,

and equip the BTSs with directional antennas of high gain to meet coverage

requirement. There are also winding highways, like roads in mountainous areas and

small towns. In these circumstances, we should set up BTSs at high places so as to

cover the villages around.


内部公开▲

When selecting antenna at the initial planning stage, we should try to select antenna

with high gain and vast coverage.


(1) Selection of antenna pattern: for BTSs to cover areas along railways and

highways, we can adopt directional antenna with narrow beam width and high antenna

gain. Besides, we can flexibly choose antenna type according to factors like landforms

and turnings on railways and highways;

(2) Selection of antenna gain: we can choose directional antenna with 17dBi－22dBi

gain; as for isotropic antenna, 11dBi;

(3) Selection of down-tilt: usually there is no need to set down-tilt for coverage of

highways, so it is recommended to use mechanically-adjustable antenna which is less

expensive. If antenna height is above 50 meters and there is request for coverage of

proximal area, we can use antenna with null fill （>15%） to avoid blind zone under

the tower.

(4) Selection of front-to-back ratio: since most subscribers within antenna coverage

on highway move fast, the front-to-back ratio shall not be too large, so as to ensure

smooth handovers.

7.4 BTS antenna selection for mountain area

Application environment feature: in remote hills or mountainous area, the attenuation of

radio wave is relatively large due to obstruction of mountains, and coverage in these

areas is a difficult issue. Normally we use large coverage, because just a small number

of subscribers scatter within the large coverage semi-diameter and call traffic volume is

low. BTSs should be set up at the appropriate locations on top of mountains, hill-side, or

mountain foot. We need to select BTS location, BTS type and antenna type based on

different subscriber dispersion and landforms. Here listed are the common situations of

BTS construction: BTS construction in mountainous basin, BTS construction on high

mountains, BTS construction on hillside, BTS construction in common mountainous

area, etc..


(1) Selection of antenna pattern: make selection based on BTS location, BTS type and


41

内部公开▲

request for coverage of around area; both directional antenna and isotropic antenna are

optional. As for BTSs on mountains, if the area to be covered is relatively low, we

should choose antenna pattern with larger vertical half-power angle to meet the

coverage needs in horizontal direction;

(2) Selection of antenna gain: use antennas with medium gain according to coverage

distance required; isotropic antenna （9-11dBi）, directional antenna （15-18dBi）;

(3) Selection of down-tilt: when we set up BTS on mountains and mountain foot area

needs to be covered, choose antenna with null fill or preset down-tilt. Amplitude of the

preset down-tilt is decided based on the relative height between the BTS and the area to

be covered. The larger the relative height is, the bigger the antenna preset down-tilt

should be.


42

内部公开▲

8 Installation & Modulation of Antenna

Knowledge point

This chapter mainly introduces the methods and essentials for installation and

adjustment of BTS antenna.

8.1 Antenna installation on Pole

8.1.1 Installation pole must be straight

Crooked pole or mishandled installation may cause the installation pole to incline,

which can affect accuracy of down-tilt and the receiving effect of isotropic antenna.

Therefore, we must first make sure installation pole is straight; a plumb bob can be

sued to check the straightness, so that we can ensure the isotropic antenna is vertical to

the ground after installation. Directional antenna’s down-tilt must be measured with tilt

meter. Take into consideration the inclination and curve of the pole when set

mechanical down-tilt.

During network planning and optimization, whether the installation pole is straight can

greatly influence the network performance. However, we often neglect to check the

straightness of the pole.

8.1.2 Lightening protection

Lightening protection must be properly handled during antenna installation, in order to

avoid lightening disturbance to BTS, and especially to antenna system on high

mountains, so as to ensure the safety of BTS structures, working staff, and equipment

inside BTS and its normal operation.

A complete lightening protection device must include:

1. lightening arrester: for controlling lightening strike point and prevent dangers to

equipment;

2. good grounding structure and earth resistance;


43

内部公开▲

3. well-designed down lead;

4. good equipotential bonding to avoid high voltage counterpunch;

5. ability to avoid high voltage surge caused by lightening.

Radio antenna should be installed within angle of protection of lightening rod (45°).

Lightening rod and down lead should be connected by welding. Material of down lead

should be galvanized flat steel (40mm×4mm). The distance between the joint of down

lead to ground net and the joint of ground lead to ground net shall be no less than 10m.

8.1.3 Diversity reception

In mobile communication, multipath transmission can cause signal fast fading, and

amplitude of level fading can reach 30dB, which means 20 times in a minute. Antenna

diversity reception skill can greatly reduce attenuation of receiving signal and improve

link quality. The principle for fixing antenna spacing interval is to ensure that different

antenna branches irrelevant to each other. Use the cross correlation coefficient of

branch signals to measure signal’s independence. Correlation coefficient of receiving

signal shall be smaller than 0.7.

Diversity distance of uni-polarized antenna

The horizontal space diversity distance for uni-polarized antenna is 20 , vertical space

diversity distance is about 15 . When BTS antenna spacing interval is fixed, increase

in antenna height can help reduce the relativity between antennas’s receiving signal.

Gain of horizontal space diversity is about 3～5dB, and gain of vertical space diversity

is about 2 ～ 4dB. Performance of horizontal space diversity is better than that of

vertical space diversity.

In actual project implementation, the horizontal diversity distance between two uni-

polarized antennas of the same sector shall be at least 10 .

Table 8-1 Horizontal diversity distance of antenna

Operating

frequency

Horizontal space diversity

distance

Vertical space diversity

distance

Min. Recommended Min. Recommended

450M 6.7m 13m 10m

800M 3.6m 7m 5.4m

1.9G 1.6m 3.m 2.4m


44

内部公开▲

2G 1.5m 3m 2.3m

8.1.4 Antenna isolation

Antenna isolation in the same system means the isolation distance between antennas of

different sectors of the same system shall be larger than 0.6m. In actual project

implementation, install antenna pole arms on the main pole bracket. The antenna is

installed on the installation pole. See Picture 8-30.

Picture 8-30 Solid diagram and vertical view of antenna

8.2 Antenna Installation on Iron Tower

In actual project implementation, install antenna on the pole arms, which are at least

1m away from the mail pole bracket. Vertical distance between antennas on different

installation poles is longer than 1m.

Generally, when installing antenna on metal towers, we shall bear in mind the

following issues:

(1) Installation of directional antenna on tower side: in order to reduce tower

antenna’s influence on antenna pattern, we should know that when the distance

between antenna center and the tower isλ/4 or 3λ/4, the antenna can get maximum

directivity;

(2) Installation of isotropic antenna on tower side: in order to reduce tower antenna’s

influence on antenna pattern, tower antenna can not be reverberator of the antenna.


45

1m

内部公开▲

Therefore, antenna shall be installed on edges or corners, and the distance between

antenna and all parts of the tower shall be longer than λ.

(3) Multi-antennas sharing tower: try as much as possible to reduce coupling effect

and cross influence between antennas of multi-bands during transmitting and receiving

signals. Try to increase isolation between different antennas; the best way is to increase

distance between them. When multi-antennas share a tower, vertical installation shall

be adopted.

8.3 Summary

The distance from antenna to tower platform: 1M;

Spacing interval between diversity reception antennas of the same cell: >3M,

Horizontal spacing interval between isotropic antennas: >4M，

Horizontal pacing interval between directional antennas：>2.5M，

Vertical spacing interval between antennas on different platforms: >1M,

Transmitting and receiving antennas shall not be installed upside down unless there is

specific direction.

Antenna shall be within the range of lightening protection.

Antenna bearing: for directional antenna, the first sector to direction of north by east

60°, the second sector to direction of due south, the third sector to north by west 60°.

Antenna down-tilt: make sure that the actual down-tilt meets the requirement of SE

planning; error difference shall be less than 2°.

Antenna perpendicularity: make sure it’s no bigger than 2°, except for BTS with

antenna down-tilt.


46

basic knowledge of antenna and antenna selection

Documents