Internal Use Only▲
Basic Knowledge of Antenna
and Antenna Selection
Edition: V1.0
Released by:
GSM Network Planning & Opti...
This document contains proprietary information of ZTE Corporation and is not to
be disclosed or used except in accordance ...
Training Materials
for GSM Network Planning & Optimization
Version Introduction
Version Date Writer Assessor Amendment rec...
Internal Use Only▲
Key words:
antenna basics、beam width、gain、tilt angle、circumstances、selection of antenna types
Abstract:...
Internal Use Only▲
Contents
Picture 1-1 Diagram of Relation between Doublet Angle and Radiation Power of
Electromagnetic W...
Picture 2-20 Diagram of comparison between BTS antenna with or without null fill effect 20........VI
Picture 3-21 Block di...
2.3.2 Vertical Beam Width....................................................................................................
7 Selection of Antenna Type..................................................................................................
Internal Use Only▲
Diagram Contents
Picture 1-1 Diagram of Relation between Doublet Angle and Radiation Power of Electroma...
Internal Use Only▲
Picture 2-20 Diagram of comparison between BTS antenna with or without null fill effect...................
Internal Use Only▲
Table Contents
Table 8-1 Horizontal diversity distance of antenna ........................................
Internal Use Only▲
1 Overview of Antenna
 Knowledge Point
 In this chapter, the radiation theory of BTS antenna and its ...
Internal Use Only▲
year of 2002 there were more than 100 manufacturers providing communication
antennas, and most of them ...
Internal Use Only▲
and fulfilling the needs of communication construction.
1.2 Theories of Antenna Radiation
Antennas must...
Internal Use Only▲
wave doublets can be adopted to form an antenna array.
Dipole with two arms of the same length is calle...
Internal Use Only▲
Picture 1-3 Half-wave Folded Dipole
1.3 Internal Structure & Types of Mobile Communication BTS
Antenna
...
Internal Use Only▲
Picture 1-4 Diagram of Directional Plate-shaped Antenna Appearing
1.3.1.1 Formation of High Gain
Pictur...
Internal Use Only▲
Picture 1-6 Apply horizontally oriented theory by adding baffle-board to one side the line
array (take ...
Internal Use Only▲
Picture 1-7 Directional plate-shaped antenna formed with several half-wave dipole
1.3.1.3 Microstrip Di...
Internal Use Only▲
Picture 1-8 Directional plate-shaped antenna consisting of several microstrip dipole
1.3.1.4 Dipole Arr...
Internal Use Only▲
Picture 1-10 Structure of Isotropic Dipole Antenna with Series Feed
This document contains proprietary ...
Internal Use Only▲
2 Concepts & Meanings of Antenna
Parameters
 Knowledge point
 This chapter mainly introduces the conc...
Internal Use Only▲
antenna gain) to 18dBi (directional antenna gain).
Antennas with around 20dBi gain and relatively narro...
Internal Use Only▲
Picture 2-13 Diagram of horizontal beam width (3dB) of BTS antenna
The gain of antenna with 20°or 30° h...
Internal Use Only▲
Picture 2-14 Diagram of BTS antenna coverage
2.3.2 Vertical Beam Width
Picture 2-15 Diagram of BTS ante...
Internal Use Only▲
2.4 Frequency Band
For different BTSs, the frequency band of antenna selected should include those
requ...
Internal Use Only▲
Picture 2-16 Common polarization mode of BTS antenna
Picture 2-17 Diagram of dual-polarization BTS ante...
Internal Use Only▲
Picture 2-18 Diagram of BTS antenna down-tilt
There are several modes of antenna down-tilt: mechanical ...
Internal Use Only▲
2.7 Antenna Front-to-back Ratio
The indicator of antenna front-to-back ratio is related to the electric...
Internal Use Only▲
2.9 Antenna VSWR
Antenna VSWR is the indicator for matching degree between antenna feed and BTS.
Defini...
Internal Use Only▲
Picture 2-20 Diagram of comparison between BTS antenna with or without null fill effect
Null fill = (ve...
Internal Use Only▲
For example, isolation between the two different polarized ports of dual-polarization
antenna, isolatio...
内部公开▲
3 Measurement of Key Antenna Indicators
 Knowledge point
 This chapter mainly introduces the measurement method, m...
内部公开▲
instruments and meters according to Picture 3 -21;
(2) Direct the measured antenna to the direction of central lobe ...
内部公开▲
3.4 Isolation Measurement of Dual-Polarized Antenna
(1) Choose standard plain antenna measurement field or chamber w...
内部公开▲
Picture 3-24 Block diagram of antenna intermodulation measurement
(2) In the operating frequency band, choose two ap...
内部公开▲
4 Antenna Parameters
 Knowledge point
 This chapter mainly introduces the engineering parameters of antenna in net...
内部公开▲
three cells in the current GSM system (mainly with ERICSSON equipment):
 Cell A: azimuth angle 0°, antenna pointing...
内部公开▲
Interference from landforms and ground objects.
Parameters at transmitting and receiving terminals include: transmit...
内部公开▲
too much traffic in one BTS. While the traffic in adjacent BTS is less due to its small
coverage and being covered b...
内部公开▲
possible, we can narrow the down-tilt, and make the maximum gain point aim at the
coverage rim. The formula of down-...
内部公开▲
5 Antenna Types
 Knowledge point
 In this chapter, we’ll get to know the classification methods of antenna, the ba...
内部公开▲
We set up different types of BTSs according to requirements of network construction;
and different types of BTSs use...
内部公开▲
The so called electrical antenna is a kind of antenna, which features in electrical down-
tilt.
The theory of electr...
内部公开▲
each of its sectors uses 3 (for space diversity, one for transmitting, two for receiving
signals). If dual-polarized...
内部公开▲
villages and suburb.
This document contains proprietary information of ZTE Corporation and is not to
be disclosed or...
内部公开▲
6 Circumstances of Antenna Application
 Knowledge point
 In this chapter, several real scene pictures are shown to...
内部公开▲
6.1 Dense Urban
Picture 6-25 Dense urban
6.2 Urban (Towns)
This document contains proprietary information of ZTE Cor...
内部公开▲
Picture 6-26 Urban (towns)
6.3 Suburb (Counties) & Villages
Picture 6-27 Suburb
6.4 Railways/ Highways (Roads)
This ...
内部公开▲
Picture 6-28 Railways & highways
6.5 Scenery Areas
Picture 6-29 Scenery areas
This document contains proprietary inf...
内部公开▲
7 Selection of Antenna Type
 Knowledge point
 Combining with the real scene pictures, this chapter introduces clas...
内部公开▲
BTS in some places and large coverage is of great importance. In this case, we need to
take into consideration aroun...
内部公开▲
cover the villages around.
When selecting antenna at the initial planning stage, we should try to select antenna
wit...
内部公开▲
(1) Selection of antenna pattern: make selection based on BTS location, BTS type and
request for coverage of around ...
内部公开▲
8 Installation & Modulation of Antenna
 Knowledge point
 This chapter mainly introduces the methods and essentials...
内部公开▲
3. well-designed down lead;
4. good equipotential bonding to avoid high voltage counterpunch;
5. ability to avoid hi...
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 an...
内部公开▲
Therefore, antenna shall be installed on edges or corners, and the distance between
antenna and all parts of the tow...
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Basic knowledge of antenna and antenna selection

  1. 1. 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.
  2. 2. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements.
  3. 3. Training Materials for GSM Network Planning & Optimization Version Introduction Version 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements.
  4. 4. Internal Use Only▲ 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements.
  5. 5. Internal Use Only▲ Contents Picture 1-1 Diagram of Relation between Doublet Angle and Radiation Power of Electromagnetic Wave 3.................................................................................................................................V Picture 1-2 Half-wave Dipole 4...................................................................................................................V Picture 1-3 Half-wave Folded Dipole 5....................................................................................................V Picture 1-4 Diagram of Directional Plate-shaped Antenna Appearing 6................................................V Picture 1-5 Vertically-set Line Array Formed by Several Half-wave Dipole 6......................................V 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............................V Picture 1-7 Directional plate-shaped antenna formed with several half-wave dipole 8........................V Picture 1-8 Directional plate-shaped antenna consisting of several microstrip dipole 9.......................V Picture 1-9 Structure of plate-shaped directional antenna array 9.........................................V Picture 1-10 Structure of Isotropic Dipole Antenna with Series Feed 10...............................................V Picture 2-11 Diagram of antenna gain in dBi and dBd 11.......................................................................V Picture 2-12 Field strength diagram of isotropic antenna and directional antenna 12........................V Picture 2-13 Diagram of horizontal beam width (3dB) of BTS antenna 13...........................................V Picture 2-14 Diagram of BTS antenna coverage 14.................................................................................V Picture 2-15 Diagram of BTS antenna vertical with 3dB beam width 14..............................................V Picture 2-16 Common polarization mode of BTS antenna 16.................................................................V Picture 2-17 Diagram of dual-polarization BTS antenna 16...................................................................V Picture 2-18 Diagram of BTS antenna down-tilt 17.................................................................................V Picture 2-19 Comparison on BTS antenna down-tilt modes 17.............................................................V This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. I
  6. 6. Picture 2-20 Diagram of comparison between BTS antenna with or without null fill effect 20........VI Picture 3-21 Block diagram of measurement of antenna gain、half-power beam width、front-to-back ratio、cross polarization discrimination 22..............................................................................................VI Picture 3-22 Block diagram of VSWR measurement 23.........................................................................VI Picture 3-23 Block diagram of antenna isolation 24................................................................................VI Picture 3-24 Block diagram of antenna intermodulation measurement 25.........................................VI Picture 6-25 Dense urban 37......................................................................................................................VI Picture 6-26 Urban (towns) 38...................................................................................................................VI Picture 6-27 Suburb 38...............................................................................................................................VI Picture 6-28 Railways & highways 39.......................................................................................................VI Picture 6-29 Scenery areas 39...............................................................................................................VI Picture 8-30 Solid diagram and vertical view of antenna 47..................................................................VI Table 8-1 Horizontal diversity distance of antenna 46.........................................................................VII 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.................................................5 1.3.1 Plate-shaped Directional Antenna...............................................................................................5 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. II
  7. 7. 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.....................................................................................................................20 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 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. III
  8. 8. 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. IV
  9. 9. Internal Use Only▲ 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 ..........................................................................................................5 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 dipole..............................8 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 2-11 Diagram of antenna gain in dBi and dBd .............................................................................11 Picture 2-12 Field strength diagram of isotropic antenna and directional antenna..............................12 Picture 2-13 Diagram of horizontal beam width (3dB) of BTS antenna.................................................13 Picture 2-14 Diagram of BTS antenna coverage.......................................................................................14 Picture 2-15 Diagram of BTS antenna vertical with 3dB beam width....................................................14 Picture 2-16 Common polarization mode of BTS antenna.......................................................................16 Picture 2-17 Diagram of dual-polarization BTS antenna.........................................................................16 Picture 2-18 Diagram of BTS antenna down-tilt .......................................................................................17 Picture 2-19 Comparison on BTS antenna down-tilt modes ...................................................................17 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. V
  10. 10. Internal Use Only▲ Picture 2-20 Diagram of comparison between BTS antenna with or without null fill effect................20 Picture 3-21 Block diagram of measurement of antenna gain、half-power beam width、front-to-back ratio、cross polarization discrimination ...................................................................................................22 Picture 3-22 Block diagram of VSWR measurement.................................................................................23 Picture 3-23 Block diagram of antenna isolation.......................................................................................24 Picture 3-24 Block diagram of antenna intermodulation measurement.................................................25 Picture 6-25 Dense urban..............................................................................................................................37 Picture 6-26 Urban (towns)...........................................................................................................................38 Picture 6-27 Suburb.......................................................................................................................................38 Picture 6-28 Railways & highways...............................................................................................................39 Picture 6-29 Scenery areas.......................................................................................................................39 Picture 8-30 Solid diagram and vertical view of antenna..........................................................................47 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. VI
  11. 11. Internal Use Only▲ Table Contents Table 8-1 Horizontal diversity distance of antenna ..................................................................................46 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. VII
  12. 12. Internal Use Only▲ 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 1
  13. 13. Internal Use Only▲ year of 2002 there were more than 100 manufacturers providing communication 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, This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 2
  14. 14. Internal Use Only▲ and fulfilling the needs of communication construction. 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- This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 3
  15. 15. Internal Use Only▲ wave doublets can be adopted to form an antenna array. 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 4
  16. 16. Internal Use Only▲ 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、 small back beam 、 reliable sealability, convenient control over depression angle of vertical pattern、and long performance life. See Picture 1-4 for antenna appearing. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 5
  17. 17. Internal Use Only▲ 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 6
  18. 18. Internal Use Only▲ 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). This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 7
  19. 19. Internal Use Only▲ 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 8
  20. 20. Internal Use Only▲ 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 9
  21. 21. Internal Use Only▲ Picture 1-10 Structure of Isotropic Dipole Antenna with Series Feed This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 10
  22. 22. Internal Use Only▲ 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 ranges from 0 to 8 dBi; that of antenna on outdoor BTS is from 9dBi (isotropic 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
  23. 23. Internal Use Only▲ 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). 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 12
  24. 24. Internal Use Only▲ Picture 2-13 Diagram of horizontal beam width (3dB) of BTS antenna The gain of antenna with 20°or 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°、180°beam width is used to cover the special-shaped sectors with extremely wide angles. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 13
  25. 25. Internal Use Only▲ 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 14
  26. 26. Internal Use Only▲ 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 ±45°bilinear 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 15
  27. 27. Internal Use Only▲ 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 16
  28. 28. Internal Use Only▲ 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 upwarp, 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 17
  29. 29. Internal Use Only▲ 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 65°angle 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 18
  30. 30. Internal Use Only▲ 2.9 Antenna VSWR Antenna VSWR is the indicator for matching degree between antenna feed and BTS. Definition of VSWR: 0.1 min max ≥= U U 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 ordinate showing the distance to the BTS, the vertical ordinate showing the ground signal strength. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 19
  31. 31. Internal Use Only▲ 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@2×43dBm, while that of the common antennas is just -130dBC@2×43dBm . 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. 2.12Isolation between Ports When multiport antenna is used, the isolation between ports shall be more than 30dB. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 20
  32. 32. Internal Use Only▲ 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 21
  33. 33. 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 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 22
  34. 34. 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 23
  35. 35. 内部公开▲ 3.4 Isolation Measurement of Dual-Polarized Antenna (1) Choose standard plain antenna measurement field or chamber without echo to install antenna according to Picture 3 -23; 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 (1) Choose standard plain antenna measurement field or chamber without echo to install antenna according to Picture 3 -24; This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 24
  36. 36. 内部公开▲ Picture 3-24 Block diagram of antenna intermodulation measurement (2) In the operating frequency band, choose two appropriate frequencies f1h and f2h , 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 25
  37. 37. 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. Based on ideal cellular communication model, directional BTS is usually divided into 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 26
  38. 38. 内部公开▲ 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: Parameters at the transmitting terminal and the receiving terminal; This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 27
  39. 39. 内部公开▲ 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: ( ) ( ) 4 1 4 1 2 1 4 1 ][D αLGGhh P P trtr r t       ≈ rP receiving power tP transmitting power rh height of receiving antenna th height of transmitting antenna rG gain of receiving antenna tG gain of transmitting antenna αL 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 28
  40. 40. 内部公开▲ too much traffic in one BTS. While the traffic in adjacent BTS is less due to its small 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 In areas like suburb、villages、highways and sea face, in order to get coverage as far as This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 29
  41. 41. 内部公开▲ 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 30
  42. 42. 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. 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 31
  43. 43. 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 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 32
  44. 44. 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; This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 33
  45. 45. 内部公开▲ each of its sectors uses 3 (for space diversity, one for transmitting, two for receiving 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 34
  46. 46. 内部公开▲ villages and suburb. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 35
  47. 47. 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 36
  48. 48. 内部公开▲ 6.1 Dense Urban Picture 6-25 Dense urban 6.2 Urban (Towns) This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 37
  49. 49. 内部公开▲ Picture 6-26 Urban (towns) 6.3 Suburb (Counties) & Villages Picture 6-27 Suburb 6.4 Railways/ Highways (Roads) This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 38
  50. 50. 内部公开▲ Picture 6-28 Railways & highways 6.5 Scenery Areas Picture 6-29 Scenery areas This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 39
  51. 51. 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 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 41
  52. 52. 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. Principles for 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 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 42
  53. 53. 内部公开▲ cover the villages around. When selecting antenna at the initial planning stage, we should try to select antenna with high gain and vast coverage. Principles for antenna selection: (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.. Principles for antenna selection: This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 43
  54. 54. 内部公开▲ (1) Selection of antenna pattern: make selection based on BTS location, BTS type and 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 44
  55. 55. 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; This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 45
  56. 56. 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 λ, vertical space diversity distance is about 15 λ. 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 λ. 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 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 46
  57. 57. 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 47 1m
  58. 58. 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. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 48

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