Basic Principles and Design of The Antenna in Mobile Communications

Document No. Product
Version
Confidentiality
V2.00
Wireless Network System Radio
Frequency Research Department
Huawei Technologies Co., Ltd.
Product Name: M900/1800 Total Pages: 37
Basic Principles and Design
Specifications of Antenna in Mobile
Communications
(Revised edition, for internal use only)
Prepared by Ai Ming Date 2001/09/08
Reviewed by Date yyyy/mm/dd
Reviewed by Date yyyy/mm/dd
Approved by Date yyyy/mm/dd
Tempus Telcosys(P) Ltd.
Time is Almighty.
www.TempusTelcosys.com

Revision Record
Date Revised
version
Description Author
1,999 1.00 Complete the first draft. Ai Ming
2000/11/9 1.00 Transfer the draft to the network planning
technical support team
Network planning technical
support team
2001/09/8 2.00 Revise the draft. Ai Ming
♦ Note:
1) The basic concepts of middle feed and bottom feeder of omni antenna are added; Sections 3.10 through
3.13 are added
2) Correct the errors in some figures. (2001-09-08)

Table of Contents
1 Overview......................................................................................................................................... 5
1.1 Antennas............................................................................................................................... 5
1.2 Development Trends of BS Antenna .................................................................................... 7
1.3 Design Concepts of BS Antenna .......................................................................................... 8
2 Basic Technologies....................................................................................................................... 9
2.1 BTS Antenna......................................................................................................................... 9
2.2 System Requirements and Antenna Technologies ............................................................ 12
2.3 Types of Antennas.............................................................................................................. 15
2.4 Design of Shaped-beam Antenna....................................................................................... 19
2.4.1 Fan Beam Antenna .................................................................................................. 19
2.4.2 Vertical Shaped-beam Antenna ............................................................................... 24
2.4.3 Beam Tilt .................................................................................................................. 25
2.5 BS Diversity Antenna.......................................................................................................... 26
2.6 Passive Inter-modulation of Base Station Antenna ............................................................ 31
2.6.1 Relationship between PIM and Receiving-transmitting Frequency ......................... 31
2.6.2 PIM Generator and Suppression Technology.......................................................... 32
3 Major Index Requirement for BS Antenna Design................................................................... 33
3.1 VSWR of BS Antenna......................................................................................................... 33
3.2 Gain (dBi)............................................................................................................................ 33
3.3 Half Power Beam Width (HPBW) ....................................................................................... 34
3.4 Front-to-Back Ratio (F/B).................................................................................................... 35
3.5 Isolation between Ports ...................................................................................................... 35
3.6 Polarization ......................................................................................................................... 35
3.7 Power Capacity................................................................................................................... 35
3.8 Zero Stuffing ....................................................................................................................... 35
3.9 Upper Side Lobe Suppression............................................................................................ 36
3.10 Beam Downtilt................................................................................................................... 36
3.11 Two-band Dual Polarization Antenna ............................................................................... 36
3.12 Two-band Dual Polarization Duplex Antenna................................................................... 36
3.13 Grounding system............................................................................................................. 37
3.14 Antenna Input Connector.................................................................................................. 37
3.15 Passive Inter-Modulation (PIM) ........................................................................................ 37
3.16 Dimensions ....................................................................................................................... 38
3.17 Weight............................................................................................................................... 38
3.18 Wind Load......................................................................................................................... 38
3.19 Working Temperature....................................................................................................... 38
3.20 Humidity............................................................................................................................ 38
3.21 Lightning Protection .......................................................................................................... 38
3.22 3-Proof Capability ............................................................................................................. 38

Basic Principles and Design Specifications of
Antenna in Mobile Communications
(Second Edition)
Key words: Mobile communications, antenna gain, design specifications
Abstract: Base station antenna is a bridge between user terminal and the Base
Station Controller (BSC). It is widely applied in the cellular mobile
telecommunications and ETS wireless telecommunication systems. This
document presents the history of antenna development, the basic antenna
technologies, and the major technical indices. Readers are expected to have an
overall understanding about the antenna of BSs in the mobile
telecommunications. The impacts of antenna lobe, antenna downtilt (mechanical
and electronic), isolation on the cell coverage and frequency reuse are also
mentioned in this document.
Abbreviation List:
Reference list
Name Author Document
No.
Release date Available place
or channel for
reference
Mobile Antenna System Manual Translated by Yang Kezhong and Jin
Shuhua
1997
Cellular Mobile Telecommunications ---
Design of BTS Antenna Feeder System
Xu Yubo 1998
Mobile Telecommunications Engineering Lu Errui, Shun Rushi, etc.
Microstrip Antenna Theory and
Engineering
Zhang Jun, Liu Kecheng, etc. 1998
Cellular Mobile Communication
Engineering Design
A. Marrola
Telecommunication Engineering Design
Manual ---- Mobile Telecommunications
Beijing Design Institute of Post and
Telecommunications Department

1 Overview
1.1 Antenna
With the rapid development of China’s economy, great changes have taken place in
the communications industry. Today, propelled by the technologies and the economic
benefits, communications industry has become one of the largest industries in China.
Major telecommunication organizations are restructured to accommodate to the rapid
development of this industry. Along with the advancement of communications industry
towards the information economy, communication is now become the key to the
sustainable development of various sectors of economy.
The development of the mobile telecommunication is even more remarkable.
Nowadays, people are no longer contented to process the information flow in fixed
places. Mobile telecommunications are in great demand when people are traveling or
on vacation. In China, the significant change of mobile telecommunications is evident.
Various types of mobile phones are everywhere bringing information about politics,
economy, culture, and life to people. The largest GSM network in China now provides
services for its over 20 million subscribers. The wireless access development is also
widely adopted to ensure the communications in rural and remote areas.
New technologies and new devices in mobile communications posed as great
challenges for antenna designers. For example, however small the terminal may be,
user would not accept the idea if the conventional antenna is attached to his portable
mobile terminal. Therefore, the antenna designers have to develop miniature or even
electronic antennas to keep up with the development of modern technologies.
In addition to small size, antenna designers have to seek more sophisticated
elements to equip the antenna with even more powerful functions such as the
diversity receiving capability, optional polarity features, and capacity to reduce the
multi-path fading. The focal point of antenna design is shifted from its physical
features (e.g. small-size, light-weight, etc.) to sophisticated electromagnetic structure,
so that antenna can play a significant role on the radio channel.
Antenna design will involve the propagation features, local environments, system
compositions and performance, Signal Noise Ratio (S/N), bandwidth features,
antenna's own mechanical structure, feasibility of production method, and the
convenience of installation. The type of the mobile communications also affects the
antenna design. The antennas used for the terrestrial system, offshore system, air
system, and satellite system differ a lot. In the cellular systems, the radiation pattern
should conform to segmentation pattern to avoid interference. In the urban areas,
diversity receiving function should be employed to offset the multipath fading.
Antennas of smaller size are required for the terminal mobile. In the design of
portable devices (e.g. the mobile phone), the antenna and Radio Frequency (RF)
front end circuit of transceiver should be integrated. Antenna unit and the equipment
should be treated as an antenna system.
In a word, the antenna should be designed as an organic party of the whole system
instead of an independent part. See Figure 1.
The design specifications described in this document only involve the base station
antenna (BS antenna) in wireless communication systems.

小型化强度 Miniaturized strength 区域距离 Distance between
regions
衰落多路径 Fading multipath 机械结构 Mechanical structure
电气指标 Electrical index 分集技术 Diversity technology
人机界面 Man-machine interface 环境 Environment
传播 Propagation 衰落 Fading
干扰 Interference 人为故障 Man-induced failure
天线 Antenna 系统 System
频率复用 Frequency reuse 多信道连接 Multi-channel connection
能力 Capability 类型 Type
陆地 Terrestrial 海事 Marine
航空 Navigation 卫星 Satellite
个人化 Customization
Figure 1 Integration of antenna and other systems

1.2 Development Trends of BS Antenna
BS antenna is the bridge between user terminal and the Base Station Controller
(BSC). It is widely applied in the cellular mobile telecommunications and ETS
wireless telecommunication systems.
The advancement of telecommunication technologies will definitely bring about the
radical change of antenna. For the mobile communication system in1970s, the omni
antennas or angle reflector antennas sufficed because the number of subscribers was
not large. A few carriers and BSs can sufficiently cover a city and satisfy the demands
of mobile telecommunications in a city.
However, mobile terminals are in great demand with the development of economy.
Old BSs can no longer meet the demands. Moreover, new types of antennas are
required as a result of the development of digital cellular technologies, so as to
improve the multipath fading, area planning and frequency reuse of the multi-channel
networks. The flat type antenna was widely adopted in the GSM digital cellular
system due to its features of low section, light structure, easy installation and
outstanding electronic performance.
From the mid1980s to the late 1990s, the unipolar antenna was used. As three
antennas were needed for one sector (see Figure 2), and a cell was usually divided
into three sectors, altogether nine antennas were needed for one cell. The large
number of antennas brought great difficulties to the construction and installation of the
base station. Under such a circumstance, the duplex polarization antenna
technologies came into being. See Figure 3.
单极化天线 Unipolar antenna 主接收 Main receiving
发射 Transmitting 分集接收 Diversity receiving
Figure 2 Configuration of unipolar antenna in one sector

Basic Principles and Design Specifications of Antenna in Mobile Communications 001
双极化天线 Bipolar antenna 主接收 Main receiving
发射 Transmitting 分集接收 Diversity receiving
双工装置 Duplex device
Figure 3 Two configurations of bipolar antenna in one sector
With channels and new BSs added, the cellular network should be adjusted and
optimized, which demands new types of BS antennas such as adaptive antennas and
intelligent antennas (The design specifications of these types will not be covered in
this document).
1.3 Design Concepts of BS Antenna
As the number of mobile communication users is increasing, the frequency allocated
to the mobile communication has been gradually raised from 30MHz to 50MHz,
150MHz, 250MHz, 450MHz, 800MHz and 1800MHz. The design of antennas has
also been changed accordingly.
The design of antennas primarily relies on some mathematical methods and
Computer Aided Design (CAD). The up-to-date method is Finite Difference of Time
Domain (FDTD), which allows the radiation structure to be of any shape and to be
made up of multiple layers of different materials. The BS antennas are usually divided
into directional antennas and omni antennas.
The BS antennas used in High Frequency (HF) and Very High Frequency (VHF) and
the omni antennas used for Ultra High Frequency (UHF) are of the line-shaped type,
which are usually analyzed and designed by the moments method. The directional
antennas used for UHF are normally the linear element antenna or paster-driven flat
type antenna.
These types of antennas can be analyzed and designed by using the element method
and Geometry Theory of Diffraction (GTD hybrid method). In fact, the latter type of
antennas can be simulated by the HFSS software of HP and Ansoft. HFSS can be
used to easily obtain the electrical specifications of this type of antennas, and then
the best design can be worked out.

The BS antenna is a kind of open field-effect radiator, which involves sophisticated
field analysis and numerical analysis. However, pure and time-consuming theoretical
analysis is not desired as antenna is intended for practical use. Designers should
accumulate experience and take the advantage of simulation software to work out the
antenna design efficiently.
As previously mentioned, the design of antenna should take the system compatibility
into consideration. System design and antenna design are closely related. A
component (functional module) may be a high performance one when viewed
independently. However, it may not be the best choice from a system point of view.
Take the printed paster antenna for example. It is less efficient than the common
dipolar antenna. But due to its small cross section and the advantage of printing
technology, it has helped turn a lot of new systems into reality. Its advantages are
evident in the application of mobile telecommunication terminal, micro cellular, radar,
and navigation equipment. Hence, antenna designer should especially take the
following factors into consideration:
Regional structure: Determine the signal coverage area and the antenna
direction.
BS antenna: the antenna height, structure, installation, down tilt requirement of
beams.
Noise level: the thermal noise and ambient noise.
Interference: the interference level, features, and co-channel interference and
neighbor channel interference.
Signal requirement: the best working frequency, bandwidth, cross interference,
and frequency reuse.
Cost of research, development, and processing.
Reliability: the technical maintenance required, installation, and installation
charges.
Vulnerability: Rust and corrosion if the antenna is installed outdoors.
User requirements
There are also some other factors that need to be considered.
The key point is designers should turn these factors into specific requirements of
hardware design and then design the antenna according to these requirements.
2 Basic Technologies
2.1 BTS Antenna
BS is widely used in the GSM digital cellular communication system, ETS wireless
access system and other terrestrial communication fields. For different fields, different
types of antennas are used, and the design specifications also differ.
In the mobile communications, the BS serves the Mobile Station (MS). Generally
speaking, it is fixed, though it also can be semi-fixed or vehicle-mounted. The
semi-fixed BS refers to the BS whose location often changes, but communication
service is not required when it is moving.

The vehicle-mounted BS is usually used in the vehicle dispatching center, which
requires communication in mobile state. The document describes only the antennas
of the fixed BSs.
Figure 4 shows the major considerations in BS antenna design. Though the antenna
design belongs to electrical design in the narrow sense, it involves with many other
fields. The most important is hardware technological conditions worked out according
to requirements of the system design.
基站天线设计 BS antenna design 电气设计 Electrical design
机械设计 Mechanical design 于无线链路有
关的设计事项
Design related to radio
link
单元和天线件设
计
Unit and antenna
component design
区域特点 Regional feature
要求的 D/U Required D/U 有无分集 Diversity requirement
频率范围 Frequency range 单元 Unit
方向图的合成 Pattern synthesis 馈电电路 Feeder cabling
无源交调 Passive
inter-modulation
风载荷设计 Wind load design
地震负载设计 Earthquake design 天线罩设计 Antenna mask design
结构件设计 Structure design 包装设计 Package design
Figure 4 Key issues in BS antenna design

To determine the hardware technical specifications, the electrical and mechanical
performance should be compared, and tradeoff between performance and cost is
necessary. In some cases, performance and cost are put in the first place, followed by
the mechanical design of electricity. Figure 5 shows the procedures of antenna
design.
基站天线设计方
法
BS antenna design 无线电链路预
估
Radio link estimation
设备结构接口 Equipment interface 硬件分析 Hardware analysis
成本预估 Cost estimation 分析数据 Analysis data
测量数据 Measurement data 各种算法 Algorithms
CAD 技术 CAM
系统要求 System requirement 频率/带宽 Frequency/bandwidth
信道/容量 Channel/capacity 业务范围 Service range
D/U 值 D/U value 成本 Cost
指标要求 Index requirement
增益 Gain 方向图 Pattern
极化特征 Polarization feature 机械性能 Mechanical feature
尺寸/总量 Dimension/weight

设计输出 Design output
结构布局 Structure layout 天线效率 Antenna efficiency
馈线网络 Feeder network 材料要求 Material requirement
电气参数 Electrical parameters 机械参数 Mechanical
parameters
成本组成 Cost composition
Figure 5 BS antenna design procedures
In practice, it is of great importance to consider how to install the antenna after the
antenna is assembled. It is because it may be much more expensive to install a BS
antenna than to produce one. Therefore, not only production cost but also an antenna
structure that allows easy installation should be taken into consideration.
2.2 System Requirements and Antenna Technologies
In the mobile communication system, the antenna helps establish the wireless
transmission connections between the wireless telephones. To ensure the
communication between the BS and the MSs within the service area, the energy of
the radio waves should radiate as evenly as possible, and the gain of the antenna
should be as high as possible.
As the width of the service area is definite, the gain cannot be raised by narrowing the
horizontal beam width. However, the vertical linear array antenna can raise the
antenna gain effectively. In the cellular system, the gain of the BS antenna is usually
between 7 dBd and 15 dBd.
Multi-channel communication is commonly used to increase the communication
capacity and improve frequency reuse ratio. This requires a wide band system with
functions of combiner and divider. At present, the frequency band of the BS devices in
China GSM cellular system is 890--960MHz. 890--915MHz is used for receiving
signals, and 935-960MHz for sending signals. The antenna relative band width is
required to be greater than 8%, and intra-band VSWR less than 1.5. When the
antenna is receiving and sending signals, passive inter-modulation will result, which in
turn increases cross interference.
With the rapid increase of the subscriber base, insufficiency of communication
channels has become a problem for urban communications. To solve this problem,
application of frequency reuse technology is strongly demanded. Though the cellular
system can reuse frequency, the effectiveness of this technology relies on the
radiation pattern of the BS antenna. The major-beam tilt and bean shaping
technologies can improve the reuse of frequency effectively.
Non-stadia transmission is one of the most common features in the mobile
communications, especially in the modern cities. The numerous high buildings in the
city constitute a complicated radio transmission environment for the mobile
subscribers and result in fading of radio transmission. The receiving electrical level is
thus affected and in some cases may fluctuate for more than 30 dB.

If the system design should be based on the lowest receiving level, the equipment
could be rather expensive. The diversity receiving technology can overcome the
fading effectively. Though application of this technology needs more devices, it is the
most cost-effective solution from the system point of view and is at the moment the
most commonly-used technology to overcome fading.
Figure 6 shows the relationship between the system requirements and the antenna
technologies.

系统要求 System requirements 高电平均匀照射业务区 Even radiation of high
level in the service
area
抑制业务区以外的辐射
（频率复用技术）
Suppression of
radiation outside the
service area
(frequency reuse
technology)
多信道宽频带 Multi-channel and
wide frequency band
稳定的接受电平 Steady receiving level 降低延迟扩展 Reduction of delayed
expansion
体积小，重量轻，抗风 Compact, light, and
wind-proof
天线技术 Antenna technology
主波束倾斜，赋形波束
综合
Integration of beam
downtilt and
shaped-beam
technologies
宽带天线单元，宽带匹
配网络
Broadband antenna
unit and broadband
matching network
分集接收 Diversity receiving 机械设计 Mechanical design
Figure 6 System requirement and antenna technology
2006-06-05 All rights reserved.www.TempusTelcosys.com

2.3 Types of Antennas
The structure or type of the BS antenna is determined by the size and landform of the
service area, and the number of cells and channels.
If the service area is within the limited range of angles on the horizontal plane, the
plat type antenna is often used. The half power beam angles of horizontal plane
include 33°, 60°, 90°, 120°, 180°, etc.
If the service area should be covered in all directions horizontally, the omni antenna is
often used, which can only tilted vertically. In the early cellular system, the length of
the antenna was determined by the gain required, and even excitation was usually
adopted for the array antennas to achieve a higher gain.
Figure 7 is the diagram of the typical structure of the omni antenna.
(a) Middle-feed mode (b) Bottom feed mode
Figure 7 Omni antenna
For the middle-feed antenna (see note 1), if the beam downtilt technology is not
applied, the maximum directivity in the direction of 0° without any tilting or declining in
the whole working frequency band.
As to the bottom-feed antenna (see note 2), however, the monotone phase variation
of every unit will cause the maximum beam directivity to change with the frequency,
which affects the network coverage seriously. When the cells should be re-divided to
achieve the effective reuse of frequency, the value of D/U is a consideration more
important than antenna gain in BS antenna design. At present, the electrical or
mechanical major-beam downtilt technology is commonly applied to the BS antenna
design in cellular mobile communications system.

Experiments show that beam downtilt can reduce the co-channel interference by
about 10dB, as shown in Figure 8. The network optimization experts have fully
realized that the beam downtilt technology is the basic technology to increase
frequency reuse because it can form appropriate array antenna radiation pattern to
compress the side lobes beside the major beam, thus reducing the frequency reuse
distance. Figure 9 shows how the BS antennas can be classified by functions and by
features.
是理想的自由方向图假
设条件下的
Ideal pattern 计算方向图 Computed pattern
接收信号强度 Strength of received signal 倾角＝3oC Downtilt=3oC
高基站距离 Distance between high
BTSs
Figure 8 Influence of beam downtilt to the frequency reuse

天线 Antenna 低旁瓣 Lower side lobe
D/U 值增加，上旁瓣被
抑制
The D/U can be
increased to suppress
the upper side lobe.
波束倾斜 Beam downtilt
零点填充 Zero stuffing 高电平 High level
业务区 Service area 干扰区 Interference area
Figure 9 Impact of side lobe on frequency reuse

基站天线 BS antenna 分集天线 Diversity antenna
单个天线 Single antenna 阵天线 Array antenna
单元天线 Unit antenna 水平面赋形波束 Shaped beam on
horizontal plane
垂直面赋形波束 Shaped-beam on
vertical plane
空间分集 Space diversity
极化分集 Polarization diversity 水平面波束控制 Beam control on
horizontal plane
多波束 Multi-beam 均匀激励 Uniform excitement
倾斜波束 E/M Beam downtilt E/M 旁瓣控制 Side lobe control
零点填充 Zero stuffing 振子，微带贴片，寄生
微带贴片
Oscillator,
micro-paster, parasitic
micro-paster
微带，缝隙，角反射器
天线
Micro-strip, slot,
corner-reflector
antenna
Figure 10 Classification of BS antenna
Note 1: Middle feeder refers to the case that the feeder point of the coaxial array omni
antenna is at the middle element. In this case, no matter how the frequency changes,
the phase change of the upper and lower elements is symmetrical, i.e., the maximum
gain of antenna is at 0°
(non-downtilt design technology).

Note 2: Bottom feed refers to the case that the feed point of the coaxial array omni
antenna is at the bottom of each element
(Bottom feed is different from the case that the power input point is at the bottom,
because the power input point of the middle-feed antenna is also at the bottom. The
difference between the middle-feed antenna and the bottom-feed antenna lies in the
actual location of the feed point). In the case of bottom feed, the phase change from
the lower to the upper elements is not symmetrical, i.e. the maximum directivity is
related with the frequency.
2.4 Design of Shaped-beam Antenna
The shaped-beam technology can increase the space frequency reuse rate. In the
cellular system, the BS antenna is required to radiate the lowest possible level to
another cell using the same frequency, but the highest possible level to the
poorly-cover area within the service area. The shaped-beam antenna falls into two
types. One is horizontal shaped-beam radiation pattern, referred to as fan beam in
engineering; another is vertical shaped-beam radiation patter, or cosecant beam.
In fact, the major-beam downtilt is not the shaped-beam technology in real sense,
though they are used for similar purpose. This document only covers the design of
shaped-beam antenna in the cellular system. For implementation of beam synthesis
and numerical technique, please refer to the related documents.
2.4.1 Fan Beam Antenna
In the metropolitan cellular system, the horizontal beam of BS antenna is not
omni-directional. The fan beam can effectively cover the service area and improve the
reuse of frequency. The typical fan beam antenna is the corner-reflector antenna. It
can adjust the beam width by controlling the angle of the reflector. Figure 11 shows
the basic geometry of the corner-reflector antenna.

偶极子 Dipole 馈电路 Feeder circuit
几何机构 Geometric
structure
H面方向图 Pattern on
horizontal plane
Figure 11 Corner-reflector antenna
In the early cellular system, this type of antenna was commonly used to get the fan
beam. However, it is now seldom used due to its defects such as less compact feeder
network, large cross section, and complicated structure. Hence, this document will
detail other types of fan beam antennas instead. These antennas are now commonly
applied to the modern cellular system. See Figure 12-a, 12-b, and 12-c.

Figure 12 HFSS simulation instance
These units are called plat antenna units due to their thin cross section. When
assembled with the appropriate antenna cover, it looks like a flat board. The formulas
used for the design of these antenna units are rather complex and the hybrid method
of MM and GTD is often resorted to. However, these methods are not suitable for an
application engineer.
To solve this problem, two American companies, Ansoft and HP, released the High
Frequency Simulation Software (HFSS) so that the answer to the electromagnetic
field problem can be found out with basic antenna principles and experience about
antenna on mind. Through the simulation of HFSS, flat antenna can change the
values of width (W) and height (H) and thus can control the half-power beam width on
the horizontal plane.
The half-wave dipole HFSS result can be controlled within the range of 55°-120° (It
can be realized in terms of structure.). To obtain a beam width between 30° and 55°,
two excitation sources should be placed in a certain interval on the horizontal
direction of the flat.
Figure 13 is the HFSS simulation result of GSM 900MHz unipolar flat unit. Designers
should be noted that the effect of antenna cover on the radiation performance should
be taken into consideration.

2.4.2 Vertical Shaped-beam Antenna
ixed to a certain height covers a limited area on
gnal level is equal in each spot of the service
As Figure 14 shows, the antenna f
horizontal plane so that the receiving si
area. To obtain shaped-beam on the vertical plane, multiple flat antennas are required
to form an array on the vertical plane. Meanwhile, appropriate amplitude and phase
feeding are required for each unit. The amplitude and phase control technology of
feeding network is very important for the beam shaping on vertical plane. The more
units there are, the more ideal shaped-beam can be obtained.
天线 Antenna 水平面 Horizontal plane
低旁瓣区 e lobeLower sid 方向图 Pattern
业务区半径 e nce areaRadius of servic
area
干扰区 Interfere
Figure 13 Shaped beam with low interference (vertical plane)

Figure 14 Pattern of antenna array with four antennas (horizontal)
Figure 15 Pattern of antenna array with four antennas (vertical)
HFSS can be firstly used to obtain the fan beam required. Its vertical pattern is
Fv( ).
Take the four-unit array for example. The amplitudes and phases of the units
numbered from 1 to 4 are represented by A1, A2, A3, A4, ф1, ф2, ф3, and ф4
respectively. The following equation can be obtained:
f( ) = Ee−jkr
r {A1e−jk( 3
2 dxCOS( )+ 1)
+ A2e−jk( 1
2 dxCOS( )+ 2)
+A3e−jk(− 1
2 dxCOS( )+ 3)
+ A4e−jk(− 3
2 dxCOS( )+ 4)
} Fv( )
Change A1, A2, A3, A4, ф1, ф2, ф3, and ф4. With the help of computer, optimization
can be done and the vertical shaped beam as shown in Figure 16 can be obtained.
The figure clearly shows the first side lobe of the symmetrical radiation pattern is
much higher.
After the shaping, the upper side lobe is obviously suppressed and is improved by 7
dB as compared with the symmetrical radiation pattern. The zero point of the lower
side lobe is stuffed and the radiation level in the service area is improved.
2.4.3 Beam Tilt
The beam tilt technology aims to tilt the major beam so that the level of the radiation
towards the frequency reuse area can be reduced. In this case, although the level of

the carrier on the boarder of the area is reduced, the interference level declines much
more than the carrier level does. It is an advantage in the system design and is
adopted worldwide by most of the cellular systems.
Figure 16
Figure (17-a) Maximum ratio combining of different correlation coefficients between
channels
The beam tilt can also be realized through electric design. That is, the downtilt of
beam can be achieved by adjusting the excitation coefficients, amplitude and phase.
A set of antenna equipped with both electric downtilt and mechanic downtilt can be
useful especially during the network optimization when the fixed electric downtilt is far
from enough.
2.5 BS Diversity Antenna
BS diversity antenna has been widely applied in the cellular systems. It can reduce
the fading when the two antennas are two wave lengths away from each other on
horizontal plane. Although receiving diversity needs two or more ports, it can
effectively reduce the fading. As a result, the BTS power is reduced and the
transmission quality is improved.

In the mobile telecommunication, the signal received will be affected seriously in
urban area with a lot of high buildings or forest with a lot trees. The fast fading is
caused by the reflection of fixed and mobile objects. Deep fading exists in a certain
part of the wave length.
In a densely-populated area, the signals received by MS at any moment contain a lot
of plane electromagnetic waves that are transmitted in parallel. The amplitudes,
phases, and angles of these electromagnetic waves are random ones. Statistically,
the amplitude and phase of one electromagnetic wave can be regarded as
independent of other electromagnetic wave. All the signal components are
synthesized into one complex standing wave, whose signal strength varies with the
change of each component.
There could be a fading of 20-30dB in a distance of several vehicles and the
existence of large amount of propagation path results in the multi-path symptom. This
kind of fading is not only found in the MS receive signal, but also BTS receive signal.
However, the multi-path fast fading disappears in the place which is ten wave lengths
away. That is, the diversity receiving can improve the communication reliability
without increasing the transmitter power or channel bandwidth.
The diversity receiving is based on one basic concept: when two or more samplings
are made for a random process, these samplings are fading independently. The
probability that all the samples are less than a fixed value is much lower than the
probability that one sample is less than this value. Hence, the comprehensive
sampling can help improve the performance of transceiver and the effect is much
better than the single sampling.
The function of synthesis is to correct the phase and delay of signals after the
multi-path transmission, add up the input signal level vectors, and add the noise at
random. So the signal-to-noise ratio after synthesis of channels is generally greater
than that of the single receiving channel. As the chance of simultaneous fading of
incoherent signals is slim, the system can be more reliable. Figure (17-b) shows how
the correlation coefficient changes with the height of the antenna and the distance.
The structure of BS diversity antenna comes into three types: space diversity, pattern
diversity, and polarity diversity. Space diversity is the most common one.
Relationship between space diversity antenna and related coefficients
To explain this relationship, one parameter is introduced, where =
hbe
d ,hbe is
the effective height of the BS diversity receiving antenna and d is the distance
between the BS diversity receiving antennas.
Figure 17-b displays the curve that illustrates the relationship between coherent of
incidence angle ( ) and .
In the urban area, as there are a lot of scatterers along the propagation path between
MS and BS, the coherent is much smaller than that in the suburb. The greater the
coherent is, the higher diversity gain will be. When the coherent is greater than 0.7,
the improvement of diversity gain is not so obvious than the case when is less than
0.7.
Figure 17-a shows that when the signal level is -10dB, the probability that the
amplitude is lower than -10dB is 1.3% ( =0.7) or 0.52% ( =0.2). That is, when the
coherent drops from 0.7 to 0.2 and the probability is improved by 0.8% only. When
both the feasibility and cost are taken into consideration in practice, it is most

appropriate to have less than 0.7. In this way, the BSs in urban area will have a
better diversity gain.
Figure 17-b also shows that when the receive signal reaches , the coherent is
affected substantially. When is equal to 0°, the coherent is the smallest and the
diversity gain is the greatest. When is equal to 90°, the coherent is the greatest,
while the diversity gain is the smallest. As the MS may move in any direction, i.e.,
could be any value within the range of 0°~90°, and the antenna will not be designed
based on the best ( =0°) case or worst case ( =90°), it is recommended to adopt the
mean value 45° for and the distance between two receive antennas is determined
by =45° and =0.7.
equaling to 45° and equaling to 0.7,With can be computed, i.e. 9. Table 1
shows the effective heights and inter-antenna spaces of the diversity antenna.
Table 2-1 Effective heights and inter-antenna spaces of the diversity antenna.( =45°, =0.7)
Effective height of
diversity antenna
(m)
20 50 70 80 90 100
Space between
antennas (m)
≥3.0 5.6 6.7 7.8 8.9 10 11.1
The following result can be obtained from the above data:
d = 0.11hbe [M]
The diversity gain is affected by the following factors: inter-antenna space, diversity
combination technology, diversity tuple, and communication probability. When the
duplex space diversity and maximum ratio combination are used, the relationship
between diversity gain and coherent can be illustrated by Figure 17-a.
For example, if the probability that the amplitude is larger than the horizontal ordinate
is 90% and =0.7, the signal level is -4.6dB and the signal level of a single Rayleigh
channel is -9.5dB. Thus, the gain of duplex space diversity is 4.9dB. The diversity
gain corresponding to other probability can be obtained in the same way.
When the antenna is placed horizontally as shown in Figure 17-c, its isolation is
determined by the antenna radiation pattern, the space, and gain.

辐射方向图 Radiation pattern 90o
方向 90o
Figure 17 Horizontal placement of antenna
Generally, the fading introduced by Voltage Standing Wave Ratio (VSWR) is not
included. If the gain of the transmit antenna on the maximum radio direction is Gat
(dBi), the level of the side lobe at the direction of 90°is SLt, the gain of the receive
antenna on the maximum radio direction is Gar(dBi), the level of the side lobe at the
direction of 90° is SLr (dBp, against the major beam. The value is negative), the
horizontal spacing is Dh, the inter-antenna isolation can be given by:
Adis = -22 - 20log (Dh/l) + (Gat + Gar) + (SLt + SLr) (dB) [negative]
If the antenna is omni antenna, SLr=SLt=0 (dB) and l in the equation is the working
wave length. (regarded as far field). Generally the SL of 65° fan beam antenna is
about -18dBp, that of 90° fan beam antenna is about -9dBp, and that of 120° fan
beam antenna is about -7dBp. The actual value can be determined according to the
antenna pattern.
Example 1: 65° fan antenna, Gat=Gar=15dBi, SLt=SLr=-18dBp,
f=915MHz,l=0.328m
Adis=-30 dB (This index must be met in GSM system.)
The following result can be obtained as per previous formula: Dh=1.25 l=0.41m
Example 2: Omni antenna, Gat=Gar=11dBi,SLt=SLr=0dBp, f=915MHz, l=0.328m
Adis=-30 dB (This index must be met in GSM system.)

The following result can be obtained as per previous formula: Dh=31.6 l=10.4m
When the antenna is placed vertically, the isolation between two antenna is
approximately:
Adis=-28-40log(Dv/l)
垂直面内辐射方向图 Radiation pattern on
vertical plane
90o
方向 90o
Figure 18 Vertical placement of antenna
Figure 18 shows the pattern space antenna for a whole cell. It is composed of four
sets of antennas, forming an angle of 90° with one another. They are used to achieve
the 180° fan bean in the omni pattern and are placed separately. The internal
between two omni antennas is 0. Thus, the difference of antenna receive power is
caused by the difference of pattern.
When the distance between the 180° fan beam antennas is 6 wave lengths, the test
shows that the correlation coefficient is less than 0.2.
Polarity diversity antenna emerges along with the rapid development of cellular
system. It integrates two orthogonal (0°/90° or +45°/-45°) polarity antennas and thus
compactness is its most remarkable feature. However, the polarization feature of
incidence angle is more likely to be vertical polarization and the average receive
power of the port of 0°/90° dual polarization antenna differs a lot. Hence, the
improvement of Signal Noise Ratio (S/N) is less obvious than other diversity
measures do. But with the +45°/-45° dual-polarization antenna, the diversity gain
equivalent to the one of space diversity antenna can be obtained.

2.6 Passive Inter-modulation of Base Station Antenna
Passive inter-modulation (PIM) is one of the major factors that generate co-channel
interference. When the antenna works in duplex mode, PIM should be considered. In
most of the cases, the PIM on transmit channel is caused by the non-linear feature of
the metal heterojunction that is found between the antenna radiation unit and the
feeder.
The co-channel interference is thus generated on the receiving branch. To enable
the concurrent transmitting and receiving, the inter-modulation power should be lower
than a standard value during the design and processing of antenna. For GSM cellular
system, this standard value is around -103 dBm.
2.6.1 Relationship between PIM and Receiving-transmitting Frequency
Suppose the frequencies of two transmit carriers are respectively Fi and Fj, the (m +
n)th
modulation is:
mFi nfjF1M=
Where, m and n are positive odd numbers and is the frequency of the
interference wave on the receiving band. The probability of the interference wave is
decided by the space between transmit power and receive power and the value of (m
+ n).
F 1M
For example, the transmit frequency of GSM 900 MHz cellular system in China falls
within the range from 935MHz to 960MHz and the receive frequency from 890 to
915MHz. The space between transmit power and receive power is 20MHz. Thus, the
PIM is of 3-order. If no effective suppression measures are taken, serious interference
will result. See Figure 19.

TX 产生 3 阶交调对 RX
的干扰
TX generates 3-order
inter-modulation that
interferes RX.
的干扰
interferes RX.
的干扰
interferes RX.
Figure 19 High-order inter-modulation and interference
The relationship between the order of PIM and the power generated can be
approximately illustrated by the formula: (m + n) × 10 dB. If the frequency space
between transmit wave and receive wave is small, 5-order or 3-order PIM will
generate interference and the level will be higher than the 7-order PIM by 20 or 40dB.
2.6.2 PIM Generator and Suppression Technology
Power generated by PIM is determined by the metal type and the structure of the
connector. PIM is mainly generated on the antenna radiator, co-axial connector,
welded joint and the contact surface that is likely to get rusted and corroded. By now,
there is no definite answer to the relationship between PIM and the structure of the
contact point.
With the rapid increase of mobile communication demand, a large number of BS
antennas are in demand, especially the duplex antenna which is more cost-effective.
The duplex antenna will be widely applied. Therefore, antenna designers should
attach more and more importance to the development of PIM suppression technology.

Table 2-2 Table 2 Basic PIM suppression methods
PIM generator Suppression method:
Radiator Use printed antenna to replace the oscillator unit
Connector Increase the contact area and use silver plate
Welded joint Reduce the number of welded joints and add solder to the
welded joint
Rust and corrosive surface Coat the surface to prevent the oxidation
Feeding network Try to use strip line or micro-strip line to replace the cable
3 Major Index Requirement for BS Antenna Design
3.1 VSWR of BS Antenna
For the BS antenna of mobile communication cellular system, the maximum value of
VSWR should be less than or equal to 1.5:1. And this requirement should be met at
the specified working frequency band and temperature range. If the input impedance
of the antenna is ZA, the nominal characteristic impedance is , the reflection
factor can be given by:
Z0
｜Г｜ =
｜ZA−Z0｜
｜ZA+Z0｜
,VSWR =
1+｜Г｜
1−｜Г｜
Where is equal to 50 . The matching feature of the port can also be
represented by the return loss:
Z0
R.L.(dB) = 20 ｜Г｜logloglog .
When VSWR is 1.5:1, the computed R.L. should be -13.98dB.
3.2 Gain (dBi)
The directivity characteristic of antenna can be depicted by the pattern. But generally
the value is used to show the concentration degree of the electromagnetic energy
radiated by antenna, i.e. directivity factor D. D is defined by the following formula:
D =
Sd
S0
｜P
∑d
=P
∑0
When the thermal loss of the antenna is considered, the antenna efficiency A
should be introduced. It is defined as follows:
A =
P
PA

P PAWhere, is the radiation power of antenna and is the input power of
antenna.
When the radiation performances of the two antennas are compared, if their input
powers remain unchanged, the antenna gain can be given by:
G = A×D
G = 10 (
(suppose the efficiency of unipole antenna is 100%).
As generally the gain is given in decibel (dB), the gain can also be given by
logloglog A×D) dBi (as compared with Isotropic antenna).
If the half-wave dipole is used as the reference antenna, the unit of gain is dBd and 0
dBd equals to 2.15 dBi (see Figure 20). Other units will not be used for the BS
antenna. Please note that the BS antenna gain refers to the gain of the working
frequency band unless otherwise specified.
实际天线 Actual antenna 半波偶极子天线 Half-wave dipole
antenna
各向同性天线 Various like
antennas
Figure 20 Relationship between dBi, dBd, ERP, and EIRP
3.3 Half Power Beam Width (HPBW)
As the BS antenna is generally erected vertically to the ground, the HPBWs of vertical
plane and horizontal plane are often used to describe the HPBW of BS antenna. The
range of HPBW should be given for the working frequency band, e.g. 65°±6°.For a

directional antenna, the included angle between the two half-power points relative to
the maximum radiant point is the half-power beam width.
3.4 Front-to-Back Ratio (F/B)
Front-to-Back Ratio (F/B) is an important factor measuring the suppression ability of
the antenna backward beam. It is the level difference between the maximum beam
and the side lobe within the range of 180°± 30° starting from 0o
. It is a positive value
in dB. F/B is associated with the antenna gain and the type of antenna and ranges
from 18 to 45 dB.
The specific index requirement is determined by the network planning and
optimization. At present, the F/B ratio of Huawei 900/1800 MHz directional antenna is
20-25dB.
3.5 Isolation between Ports
There are various types of multi-port antennas, such as dual polarization antenna,
two-band dual polarization antenna, two-band dual polarization duplex antenna.
When they work in duplex mode, the isolation between ports should be greater than
30dB.
3.6 Polarization
Polarization refers to the orientation of electric filed vector radiated by the antenna on
the space. The linear polarization antenna is often adopted for the BS.
With the ground as the reference plane, if the electric field vector is vertical to the
ground, it is called Vertical Polarization (VP).
If the electric field vector is parallel to the ground, it is called Horizontal Polarization
(HP). The dual polarization antenna often adopts the +45° and -45° cross dual-line
polarization.
3.7 Power Capacity
Power capacity here refers to the average power capacity. Antenna is composed of
matching device, balancing device, phase-shifting device, and other coupling device.
The power it can bear is limited. Based on the actual maximum input power of BS
antenna (Single carrier power is 20W.), if one antenna port can receive maximum 6
carriers, the antenna input power should be 120W. Thus the power capacity per
antenna port should be greater than 200W when the temperature is 65°
C.
3.8 Zero Stuffing
When shaped-beam design is adopted in the vertical surface of base station
antennas, the first zero point of the lower side lobe need to be stuffed without any
obvious depth, so as to make the radiant level more even within the service area.
Usually, if the zero depth is greater than -26dB in relation to major beam, this means
the antenna has zero stuffing.

1)
2)
3)
3.9 Upper Side Lobe Suppression
To enhance the frequency reuse efficiency and reduce the co-channel interference to
adjacent cells in a microcell cellular system, the base station antenna beam can be
shaped based on some principles.
That is, those side lobes that aim at the interference area should be lowered as much
as possible, and the D/U value (ratio of strengths of desired and undesired signals)
should be increased, and the level of the upper side lobe should be less than -18dB.
There is no such a requirement for macrocell base station antennas
3.10 Beam Downtilt
Antenna downtilt needs to be adjusted to meet the coverage requirement or network
optimization requirement. However, if the downtilt is adjusted mechanically, when the
downtilt is adjusted by an angle of more than 8°, the horizontal beam width of base
station antenna will loss its shape, which affects the sector coverage. At present,
there are following types of beam downtilts:
Fixed beam electronic downtilt. By adjusting the amplitude and phase of radiator,
the antenna major beam can deviate from the normal direction of the antenna
array element for a certain angle, e.g. 3°, 6°, or 9°. When used together with
mechanical downtilt, electronic downtilt allows an adjustable range of antenna
downtilt angle of 18-20°.
Manual-adjustable beam electronic downtilt. The adjustable phase-shifter can be
adopted for the BS antenna, so that the direction of the main bean can be
adjusted continuously within the range of 0-10° (not including the mechanical
adjustment).The major suppliers of this type of antenna include
HUBER-SUNNER and ALLEN DB.
Remote-control beam electronic plunge angle. This type of base station antenna
is equipped with micro servo system. The phase shifter can be controlled by the
precision electric engine so as to remotely control the program. However, the
addition of active control circuit degrades the reliability of antenna and
complicates the lightening-proof problem. DELTEC (New Zealand) is one of the
major suppliers of this type of antenna.
3.11 Two-band Dual Polarization Antenna
It is a new type of antenna that integrates the antennas of two bands, e.g., GSM/DCS,
GSM/WCDMA and DCS/WCDMA. See figure 21.
3.12 Two-band Dual Polarization Duplex Antenna
To reduce the feeders, duplexer (in fact it is a filter combiner) is used to combine the
two powers with the same polarization but different frequency into one. See Figure
21.

双频双极化天线 Two-band dual
polarization antenna
双频双工双极化天线 Two-band dual
polarization duplex
antenna
GSM 天线单元 GSM antenna unit DCS 天线单元 DCS antenna unit
滤波合路器 Filtering combiner
Figure 21 Multi-port antenna
3.13 Grounding system
BS antenna is normally installed on a high position. To prevent the lightning strike, the
DC resistance between inner and outer conductors of antenna port should be
designed as 0.
3.14 Antenna Input Connector
To reduce the passive inter-modulation and ensure the RF connection, the input
connector of antenna adopts 7/16DIN-Female. Before the antenna is used, the
connector should be properly capped to avoid the oxidation and the intrusion of
impurities.
3.15 Passive Inter-Modulation (PIM)
To reduce the noise resulting from the non-linearity of antenna, the PIM of antenna
should be less than -103dBm (2x10W).

3.16 Dimensions
To facilitate the storage, transportation, installation, and ensure the security, so far as
the electrical indices are satisfied, the size of antenna should be as small as possible.
3.17 Weight
To facilitate the storage, transportation, installation, and ensure the security, so far as
the electrical indices are satisfied, the antenna should be as light as possible.
3.18 Wind Load
As BS antennas are usually installed on high buildings and towers, it is required that
an antenna should work normally when the wind speed is 36m/s, and remain
undamaged when it is 55m/s, especially in coastal areas where the wind is usually
strong.
3.19 Working Temperature
A BS antenna should work normally when the environmental temperatures is between
-40°C and +65°C.
3.20 Humidity
A BS antenna should work normally when the environmental relative humidity is
between 0 and 98%.
3.21 Lightning Protection
Direct DC grounding is required for all the radio frequency input ports of a BS
antenna.
3.22 3-Proof Capability
A base station antenna should have a 3-proof capability, namely, humidity-proof, salt
fog-proof and mould-proof. A base station omni-antenna should allow upside-down
installation, and should satisfy the 3-proof requirement as well.

Basic Principles and Design of The Antenna in Mobile Communications

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Basic Principles and Design of The Antenna in Mobile Communications