WCDMA RNP Antenna Type Selection Guidance-20040716-A-1.0

Product name Confidentiality level WCDMA RNP For internal use only

Product version V100R001

Total pages 33

WCDMA RNP Antenna Type Selection

Guidance For internal use only

Prepared by: URNP-SANA Date: 2003-07-23 Reviewed by: Date: Reviewed by: Date: Approved by: Date:

HUAWEIHUAWEI

Huawei Technologies Co., Ltd. All rights reserved

WCDMA RNP Antenna Type Selection Guidance For Internal Use Only

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Revision record

Date Revision version

Description Author

2003-08-06 1.00 Initial transmittal Gu Jufeng


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Table of Contents

1 Overview ............................................................................................................................... 6 1.1 Antenna Classification ..................................................................................................... 6 1.2 Major Technical Performances of the Antenna................................................................ 6

1.2.1 Working Bands........................................................................................................... 6 1.2.2 Antenna Gain............................................................................................................. 7 1.2.3 Antenna Pattern ......................................................................................................... 8 1.2.4 Relationship between Wave Width and Gain............................................................. 9 1.2.5 Polarization Mode .................................................................................................... 11 1.2.6 Downtilt .................................................................................................................... 12 1.2.7 Voltage Standing Wave Ratio (VSWR) .................................................................... 12 1.2.8 Port Isolation............................................................................................................ 13 1.2.9 Power Capacity........................................................................................................ 13 1.2.10 Input Interface of the Antenna ........................................................................ 14 1.2.11 Passive Inter-modulation (PIM) ...................................................................... 14 1.2.12 Antenna Size and Weight ............................................................................... 14 1.2.13 Wind Load ...................................................................................................... 15 1.2.14 Working Temperature and Humidity ............................................................... 15 1.2.15 Lightning Protection........................................................................................ 15 1.2.16 Three-Proof Capability.................................................................................... 15

2 Principles for Antenna Type Selection................................................................................. 16 2.1 Principles for Selection of Antenna Working Bands....................................................... 16 2.2 Principle for Antenna Gain Selection ............................................................................. 16 2.3 Principle for Antenna Beam Width Selection ................................................................. 17 2.4 Principle for Polarization Mode Selection ...................................................................... 17 2.5 Principle for Downtilt Mode Selection ............................................................................ 18

2.5.1 Comparison between Mechanical Downtilt and Electricity Downtilt ......................... 18 2.5.2 Comparison between Preset Electricity Downtilt and Zero-Point Filling................... 20 2.5.3 Planning and Optimization of Downtilt Angle ........................................................... 21

2.6 Principle for Front-to-back Ratio Selection .................................................................... 21 2.7 Principle for Antenna Size Selection.............................................................................. 22 2.8 Principle for Antenna Impedance Selection ................................................................... 22 2.9 Principle for Antenna Selection at Special Occasions ................................................... 22

3 NodeB Antenna Type Selection at Different Scenarios ....................................................... 24 3.1 NodeB Antenna Type Selection for Urban Coverage .................................................... 24 3.2 NodeB Antenna Type Selection for Suburb Coverage................................................... 25 3.3 NodeB Antenna Type Selection for Rural Areas............................................................ 26 3.4 NodeB Antenna Type Selection for Highway Coverage ................................................ 27 3.5 NodeB Antenna Type Selection for Rural Coverage...................................................... 28 3.6 NodeB Antenna Type Selection for Offshore Coverage ................................................ 29 3.7 NodeB Antenna Type Selection for Tunnel Coverage ................................................... 30 3.8 NodeB Antenna Type Selection for Indoor Coverage.................................................... 31


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List of Figures

figure 1 Relationship between dBi and dBd ............................................................................ 7 figure 2 The horizontal and vertical patterns of a directional antenna..................................... 8 figure 3 The relationship between antenna gain and beam widths ....................................... 11 figure 4 Changes of the horizontal pattern in case of different downtilt angles ..................... 19 figure 5 Different influences of different downtilt modes on back lobe .................................. 19 figure 6 The 8-figure-shape omni antenna pattern (horizontal) ............................................. 23 figure 7 Heart-shape omni antenna pattern (horizontal)........................................................ 23


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WCDMA RNP Antenna Type Selection Guidance

Key words: WCDMA, NodeB, Antenna Type Selection Abstract: This article describes the major technology indices of antennas and type

selection methods in applications from the network planning point of view. It also describes principles and suggestions for the antenna type selection in different application environments.

List of abbreviations:


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1 Overview

Antenna is the interface between a radio transceiver and outside propagation

environment. The same set of antenna can both emit and receive radio waves.

When emitting radio waves, it converts the high-frequency currents into

electromagnetic waves; when receiving radio waves, it converts electromagnetic

waves into high-frequency currents.

Network coverage is finally realized through antennas. Therefore, the network

coverage quality and interference control depend largely on the correctness of

antenna type selection.

1.1 Antenna Classification

Similar with antennas of GSM base stations, WCDMA antennas can also be

divided into omni antennas and directional antennas according to the emission

direction.

Based on the polarization mode, antennas can be divided into vertical

polarization antennas (also called mono-polarization antennas) and cross

polarization antennas (also called dual polarization antennas).

According to the outlines, antennas can be divided into whip antennas, plate

antennas and cap antennas.

1.2 Major Technical Performances of the Antenna

The technical performances of an antenna include: working bands, gain,

polarization mode, beam width, preset downtilt, the downtilt mode, the downtilt

adjustment range, front-to-back ratio, side lobe suppression ratio, zero-point

filling, return loss, power capacity, impedance and third order intermodulation.

The mechanical performances include: size, weight, antenna input interface and

wind load.

1.2.1 Working Bands

The FDD working bands of WCDMA system:

i For Europe and China

Uplink: 1920 ~ 1980 MHz

Downlink: 2110 ~ 2170 MHz

ii For North America


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Uplink: 1850 ~ 1910 MHz

Downlink: 1930 ~ 1990 MHz

1.2.2 Antenna Gain

As a passive device, antenna itself cannot increase the energy of emitted signals.

It only can centralize the energy to a certain direction by combining the antenna

dipoles and changing their feeding mode. Gain is one of the most important

indices of an antenna. It indicates the antenna’s capability of centralizing energy

to a certain direction. Two units are often used to present antenna gain: dBi and

dBd. The relationship between them is shown as follows:

0 2.15dBd dBi= (1.1)

dBi is defined as the energy centralizing capability of the actual directional

antenna (including omni antenna) in relation to isotropic antennas. “i” stands for

“isotropic”.

dBd is defined as the energy centralizing capability of the actual directional

antenna (including omni antenna) in relation to dipole antennas, and “d” stands

for “dipole”.

The relationship between the two units for antenna gain is illustrated as follows:

¸ Isotropic

DipoleActual antenna

The actual antenna gain is 11dBi

11dBi

8.85dBd 2.15dBi 2.15dBi ERP

EIRP

figure 1 Relationship between dBi and dBd

The antenna gain is not only related to the quantity of dipole units, but also

related to the horizontal beam width and vertical beam width.


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1.2.3 Antenna Pattern

The graph describes the distribution of electromagnetic field of the antenna

emission along the fixed distance on the angular coordinates is called pattern. A

pattern presented by emission field intensity is called field intensity pattern, a

pattern presented by power density is called power density pattern, and a pattern

presented by phase is called phase pattern.

The antenna pattern is a three-dimension graph, but it usually appears as two

patterns in two planes perpendicular to each other, called plane patterns. In

general, they are called vertical pattern and horizontal pattern. Horizontal

patterns are divided into omni antenna horizontal pattern and directional antenna

horizontal pattern. There are some special directional antennas such as

heart-shape antenna and 8-figure-shape antenna.

The directionality of an antenna is obtained by means of arrangement of dipoles

and change of the feeding phase of each dipole. This is very similar to the

interference effect of light. Therefore energy will be enhanced in certain

directions, while weakened in other directions, forming lobes (or beams) and

zero-points. The lobe with the strongest energy is called main lobe, the upper

and lower lobes with the second strongest energy are called first side lobes, and

so on. In case of directional antennas, back lobes exist. The horizontal and

vertical patterns of a directional antenna are as follows:

Side lobes

Zero points

Main lobe

Main lobe max value

Zero-point filling

Back lobe

Horizontal semi-power angle

Horizontal pattern -3dBVertical pattern

5dB/scale

Front-to-rear ratio

5dB/scale

figure 2 The horizontal and vertical patterns of a directional antenna

The beam width (also called semi-power angle) includes the horizontal beam

width and vertical beam width. They are defined as the beam width between two

points in horizontal direction and vertical direction respectively which the power

are half of the max emission power. Common horizontal beam widths of NodeB

antenna include 360°, 90°, 65°, 60° and 33°, and common vertical beam widths


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include 6.5°, 7°, 10°, 13° and 16°.

Front-to-back ratio: It refers to the signal emission strength ratio between the

main lobe direction and back lobe direction, namely the difference between the

side lobe level beam within 180 ± 30° of the antenna backward direction and the

maximum beam, presented by a positive value. In general, the front-to-back ratio

is within 18 ~ 45dB. For dense urban areas, antennas with large front-to-back

suppress ratios should be used in priority.

Zero-point filling: In case of shaped beam design in the vertical plane of a

NodeB antenna, in order to make the emission level in service area more

uniform, the first zero-point of lower side lobe should be filled so that no obvious

zero depth exists. As the vertical beam width of high-gain antenna is narrow, the

nearby coverage of such antennas in particular should be improved by means of

the zero-point filling technology. If zero depth is greater than -26dB in relation to

the main beam, it means that zero-point filling is used. Some suppliers use

percentage to represent zero-point filling. For example, if the value of zero-point

filling is 10%, the relationship between these two methods is shown as follows:

( ) ( )20 lg % 100%Y dB x= ⋅ (1.2)

For example: If zero-point filling is 10%, X=10, then

( )20 lg 10% 100% 20 dBY = ⋅ = −

Upper side lobe suppression: As for a micro cell system, in order to improve

the efficiency of frequency reuse and reduce co-frequency interference to

adjacent cells, during beam shaping, we should reduce as much as possible the

upper side lobes that affect adjacent cells and enhance the D/U value (strength

ratio between useful and useless signals). The first upper side lobe level should

be less than -18dB in relation to the main beam. As for a macro cell system,

there is no such a requirement.

1.2.4 Relationship between Wave Width and Gain

An antenna is an energy-centralizing device. The enhancement of emission in

one direction means the reduction of emission in other directions. In general, we

can enhance the emission strength in a certain direction by reducing the

horizontal lobe width so as to increase the antenna gain. Under a given antenna

gain, the horizontal beam width is in reverse proportion with the vertical beam

width, as shown below:

( )10 lg 32400aG θ β≈ ⋅ ⋅⎡ ⎤⎣ ⎦ (1.3)


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Where, Ga refers to antenna gain, unit: dBi;

β refers to the vertical beam width, unit: degree .

Θ refers to the horizontal beam width, unit: degree.

Based on the formula above, when we already know the gain and horizontal

beam width of an antenna, we can estimate its vertical beam width.

For example: If the gain of an omni antenna is 11dBi, and the horizontal beam

width is 360°, the vertical beam width is:

1.1

32400 7.15360 10

oβ = =⋅

(1.4)

Because of differences in design and manufacturing, the actual vertical beam

width of omni antenna is usually smaller than that of calculation result. The less

the difference, the better the design.

Take a dipole antenna as example, the relationship among antenna gain, vertical

beam width and horizontal beam width is shown as follows:


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Gain (dB)

Vertical

Horizontal semi-power lobe width

figure 3 The relationship between antenna gain and beam widths

Therefore, when the antenna gain is low, the vertical beam width and the

horizontal beam width are usually big; when the antenna gain is high, the vertical

beam width and the horizontal beam width are usually small.

In addition, the antenna gain depends on the number of dipoles. The more

dipoles, the higher gain and bigger aperture of the antenna ( the effective

receiving area). For omni antennas, when the gain increases by 3dB, the

antenna length increases by one time. Therefore the gain of omni antenna will

not exceed 11dBi generally.

1.2.5 Polarization Mode

Polarization is the emission performance describing the vector direction of field

intensity of electromagnetic wave. Unless otherwise specified, the space


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direction of electric field vector is the polarization direction of electromagnetic

wave. Here, the vector direction refers to the direction of maximum emission of

the antenna.

If the space direction of the electric field vector does not change at any time, the

electromagnetic wave is called linear polarization wave. With the ground as

reference, if the electric field vector is parallel to the ground, the electromagnetic

wave is called horizontal polarization wave. Sometimes, the electric field vector

is not fixed, and the pathway that the vector endpoint works out is a circle. In this

case, the electromagnetic wave is called round polarization wave. If the pathway

is an ellipse, the wave is called elliptic polarization wave. Both elliptic polarization

wave and round polarization wave have the rotating feature.

The electromagnetic waves of different bands propagate in different polarization

modes. Mobile communications systems usually use vertical polarization, while

the broadcast systems usually use horizontal polarization. Elliptic polarization is

generally used in satellite communication systems.

Two polarization modes of WCDMA antennas include single polarization and

dual polarization. They both fall in linear polarization. Single polarization

antennas in WCDMA system adopt vertical polarization, while dual polarization

antennas use polarization diversity to minimize the negative effect of multi-path

fading in the mobile communication system so as to improve the quality of

receiving signals. Dual polarization antennas in the WCDMA system usually use

the ± 45° cross polarization mode.

1.2.6 Downtilt

Antenna downtilt is an important method to strengthen the signal level of the

main service area and reduce interference to other cells. The downtilt modes

include mechanical downtilt, preset electricity downtilt and adjustable electricity

downtilt (electrically controlled antenna). Mechanical downtilt refers to setting the

downtilt angle by adjusting the antenna support to let the antenna down to a

certain position. Electricity downtilt refers to controlling the downtilt angle by

changing the phase of the dipole. The downtilt angle of a preset electricity

downtilt antenna cannot be changed after the antenna leaves the factory, while

the downtilt angle of an electrically controlled antenna can be changed.

Mechanical downtilt and electricity downtilt can be applied together.

1.2.7 Voltage Standing Wave Ratio (VSWR)

In a NodeB antenna of a mobile communications cellular system, the maximum


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VSWR should be below 1.5:1. Assume that ZA is the input impedance of antenna

and Z0 is the nominal characteristic impedance (Z0 of WCDMA antenna is 50Ω),

then the reflection coefficient is:

0

0

A

A

Z ZZ Z

−Γ =

+ (1.5)

11

VSWR+ Γ

=− Γ

(1.6)

Return loss (R.L.) can also indicates the matching characteristic of the port.

Return loss is calculated as follows:

. .( ) 20 lgR L dB = ⋅ Γ (1.7)

When VSWR is 1.5:1, R.L. is 13.98dB.

When the input impedance is not consistent with the characteristic impedance,

the reflected wave and the incident wave overlap on the feeder and form

standing wave. The ratio between the maximum value and the minimal value of

the adjacent voltage is VSWR. If the VSWR is too big, the communications

distance will be shortened, and the reflection power will return to the power

amplifier of the transmitter and burn out the power amplification tube.

1.2.8 Port Isolation

For multi-port antennas, such as dual polarization antennas, and dual band and

dual polarization antennas, in case of transmission-receiving sharing, the

isolation between ports should be greater than 30dB. For the case of intersystem

sharing, the isolation between intersystem ports should more than 30dB.

Normally, more than 40dB is recommended.

1.2.9 Power Capacity

It refers to the average power capacity. An antenna includes coupling devices

such as matching device, balancing device and phase shift device. Their bearing

power is limited. In view of the actual maximum input power of NodeB

(single-carrier power is 20W), if one port of the antenna supports the input of 4

carriers, then the maximum input power of the antenna will be 80W. Therefore,

the single-port power capacity of the antenna should be greater than 150W

(When the ambient temperature is 65°C).


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1.2.10 Input Interface of the Antenna

In order to improve the reliability of passive inter-modulation and RF connection,

the input interface of NodeB antennas should be 7/16 DIN-Female type. Before

an antenna is put into use, there should be a closure cap at the port to prevent

oxidation and ingression of impurities.

1.2.11 Passive Inter-modulation (PIM)

The passive inter-modulation characteristic refers the inter-modulation effect

caused by the passive components such as connector, feeder, antenna and filter

due to the non-linearity of the components themselves when they work under the

condition of high-power signals of multiple carriers. In general, the passive

components are considered to be linear, but under high-power conditions, all

passive components are somewhat non-linear. The causes are as follows:

Metals made different materials contact one with another, the contact surface

of the same material is not smooth, the connection is not firm; and magnetic

materials exist.

The existence of inter-modulation product will produce interference to the

communications system. Especially the inter-modulation product within the

receiving band will have bad impact on the receiving performance of the system.

So there are strict specifications for the inter-modulation characteristic of passive

components such as connectors, cables, and antennas. The requirements are as

follows: The passive inter-modulation index of connector is ≤ -150dBc, the

passive inter-modulation index of cables is ≤ -170dBc, and the passive

inter-modulation index of antennas is ≤ -150dBc.

1.2.12 Antenna Size and Weight

In order to facilitate storage, transportation and installation and ensure the safety,

an antenna should be smaller in size and more light in weight while it meets all

the electric indices.

At present, operators are more and more picky about the size, weight and

appearance of antennas. So when selecting antennas, we should pay special

attention not only to the technical performance indices, but also to those

non-technical factors. NodeB antennas in urban areas should be small in size

and light in weight and eye attracting, while there are no such a requirements for

antennas in the suburbs and rural areas.


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1.2.13 Wind Load

NodeB antennas are usually installed on top of high buildings or iron towers,

where the wind is very strong all the year, especially in coastal areas. Therefore

antennas should be able to work normally at the wind speed of 36m/s and should

not be damaged at the wind speed of 55m/s.

Antennas themselves can normally endure strong wind. In areas with strong

wind, antennas are usually damaged because of reasons of iron towers or

mono-poles. Therefore in such areas, antennas with small surface area should

be used.

1.2.14 Working Temperature and Humidity

NodeB antennas should be able to work normally at the environment

temperature range of -40°C to 65°C and within the relative humidity range of 0 to

100%.

1.2.15 Lightning Protection

All the RF input ports of antennas must be grounded directly with DC.

1.2.16 Three-Proof Capability

NodeB antennas should have the three-proof capability, namely: damp proof,

salt mist proof and mould proof. Omni antennas must support upside-down

installation and meet the three-proof requirements.


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2 Principles for Antenna Type Selection

2.1 Principles for Selection of Antenna Working Bands

1） Outdoor Antennas

Outdoor antennas should be wideband antennas those work at the 1710 ~

2170MHz band. The use of wideband antennas is helpful to reduce the number

of antennas (reduce the procurement cost) while such antennas can serve both

WCDMA and DCS systems simultaneously.

Although wideband antennas are selected exclusively, for urban coverage, the

strategies and principles for WCDMA network optimization are largely different

from those for DCS1800. If the WCDMA and DCS systems share antennas,

there will be mutual influences in the optimization of the two systems. Therefore,

for urban coverage, antenna sharing for WCDMA and DCS systems is not

recommended.

2） Antennas of Indoor distribution system

In general, indoor distribution systems all involve antenna sharing requirement,

so the compatibility between forward (GSM/DCS) and backward (WLAN) should

be considered in antenna selection. Therefore the antennas for indoor

distribution systems should be wideband antennas (800 ~ 2500 MHz).

For Green Field operators like China Telecom, wideband antennas are also

recommended. An important reason is that DCS bands after clearing may be

adopted in new mobile communications modes in the future.

2.2 Principle for Antenna Gain Selection

The gain of outdoor omni antennas is usually within the range of 2~11dBi, the

gain of indoor omni antennas is usually within the range of 0~8dBi, and the gain

of outdoor directional antennas is within the range of 3~22dBi.

Low-gain antennas are usually used for micro cellular networks for indoor

coverage and coverage of outdoor hot spots. This kind of antenna is small in size

and easy to install.

Mid-high-gain antennas are suitable for urban areas (the system simulation

results from HUAWEI network planning department shows that antennas with

higher gain can better control interference). The horizontal lobe width of this kind

of antennas is generally 65°.


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High-gain antennas are suitable for wide coverage. They are applied for

coverage of highways, railways, tunnels and long and narrow landforms. The

horizontal lobe width of this type of antennas is normally 33° or lower, resulting in

many zero-points. Therefore, if the antenna installation height is very high,

antennas with zero-point filling or preset electricity downtilt should be selected to

avoid zero-point depth effect on the near-end coverage (tower-bottom shadow

effect). In addition, this type of antenna has many dipoles and the volume is very

large, so we should pay attention to the install ability and wind load.

2.3 Principle for Antenna Beam Width Selection

Selection of beam width includes selection of width of horizontal beam and

vertical beam, which are closed related. The horizontal beam width depends on

the type design of NodeB, while the vertical beam depends on antenna gain.

In urban areas, for 3-sector vertex-excited NodeBs, antennas with 65° horizontal

beam width are recommended. For 6-sector vertex-excited NodeBs, antennas

with 33° horizontal beam width are recommended. In suburbs, for 3-sector

center-excited NodeBs, antennas with 90° horizontal beam width are

recommended.

After determining the horizontal beam width, select the vertical beam width

based on the requirements for gain and interference control. The narrower the

vertical lobe is, the higher the antenna gain will be, and the better the

directionality will be (it is easier to control interference). However, the zero-point

depth will be more obvious. The preset electricity downtilt technology and

zero-point filling technology should be used to solve the zero-point problem. If

the narrower the vertical lobe is, the longer, heavier and more expensive the

antenna will be. In this case, we should consider the installation ability of the

antennas.

2.4 Principle for Polarization Mode Selection

Comparison between vertical single polarization antennas and vertical dual

polarization antennas: From the signal emission point of view, mobile stations

match the vertical polarization signals more easily because perpendicular to the

ground; vertical single polarization antennas give better coverage effect than any

other non-vertical polarization antennas, especially in open mountainous areas

and rural areas. Tests show that the vertical polarization antennas give better

coverage effect than dual polarization (±45°) antennas in open mountainous

areas and rural areas. However, in urban areas, due to large number of dense


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buildings, the electromagnetic waves are reflected from the surfaces of the

buildings many times. Metal objects and metal oxide film plated glass all cause

polarization rotation, so there is no obvious difference between vertical

polarization antennas and ±45° polarization antennas in the coverage ability.

From the receiving point of view, because two vertical polarization antennas

must be for diversity receiving, while only one dual polarization antenna can do

this, so single polarization antennas need more installation space and more

maintenance work than dual polarization antenna do. In addition, there is no

difference between space diversity gain and polarization diversity gain in urban

areas. As the antenna size is concerned, even if dipoles with different

polarization directions in a dual polarization antenna overlap together, and

enough isolation can be ensured, so a dual polarization antenna is not bigger

than a single polarization in size.

Suggestion: For urban coverage, ±45° dual polarization antennas are preferred;

for suburbs, rural areas and highways, vertical polarization antennas are

preferred.

2.5 Principle for Downtilt Mode Selection

2.5.1 Comparison between Mechanical Downtilt and Electricity Downtilt

Three kinds of methods and their combinations are usually used for antenna

beam downtilt: Mechanical downtilt, preset electricity downtilt and electrically

controlled downtilt (for electrically controlled antennas). During adjustment of the

electrically controlled antenna downtilt angle, the antenna itself will not move, but

the phase of the antenna dipole is adjusted through electricity signals to change

the field intensity so that the antenna emission energy deviates from the

zero-degree direction. The filed intensity of the antenna is increased or

decreased in each direction so that there will be little change in the antenna

pattern after the downtilt angle is changed. The horizontal semi-power width is

unrelated with the downtilt angle. However, during mechanical adjustment of the

downtilt angle, the antenna itself will be moved. It is necessary to change the

downtilt angle by adjusting the location of the back support of the antenna. When

the downtilt angle is very large, although the coverage distance in the main lobe

direction changes obviously, yet signals in the direction perpendicular to the

main lobe almost keep not change, the antenna pattern deforms seriously, and

the horizontal beam width becomes greater as the downtilt angle is increased. A

preset downtilt antenna is similar to an electrically controlled antenna in working


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principle, but a preset angle can not be adjusted.

The advantages of an electrically controlled antenna are as follows: When the

downtilt angle is very large, the coverage distance in the main lobe direction will

be shortened obviously and the antenna pattern will not remarkably change, so

the interference can be reduced. On the other hand, mechanical downtilt may

deform the pattern. The larger the angle is, the more serious the deformation is.

Hence it is difficult to control the interference. The change of horizontal patterns

under the two adjustment modes is shown in Figure 4. Certainly, it is related to

the vertical beam width.

Mechanical downtilt Electr. downtilt

figure 4 Changes of the horizontal pattern in case of different downtilt angles

In addition, electrically controlled downtilt and the mechanical downtilt have

different influence on the back lobe. Electrically controlled downtilt allows further

control of the influence on the back lobe, while mechanical downtilt enlarges the

influence on the back lobe, as shown in Figure 5:

Back lobe peak value

Back lobe peak value

Horizontal pattern

Horizontal pattern

Mechanical downtilt

Electr. downtilt

Main lobe peak value

Main lobe peak value

Rotation axis

figure 5 Different influences of different downtilt modes on back lobe

If the mechanical downtilt angle is very large, the emission signals of the antenna

will propagate to high buildings in backward direction through the back lobe, thus


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resulting in additional interference.

In addition, during network optimization, management and maintenance, when

we need to adjust the downtilt angle of an electrically controlled antenna, it is

unnecessary to shut down the entire system. So we can monitor the adjustment

of the antenna downtilt angle using special test equipment for mobile

communication, so as to ensure the optimum value of the downtilt angle value of

the antenna. The step degree of downtilt adjustment of an electrically controlled

antenna is 0.1°, while that of a mechanical antenna is 1° or bigger. After

installing an electrically controlled antenna, the maintenance personnel can

adjust the downtilt angle on the ground, without climbing to the antenna

installation position. The maintenance personnel can also monitor and adjust

remotely NodeB antennas on high mountains and in remote areas. During

mechanical adjustment of the downtilt angle, the power amplifier of the cell

should be shut down. Monitoring cannot be carried out during adjustment of the

downtilt angle. The downtilt angle of a mechanical antenna is a theoretical value

calculated by means of computer simulation and analysis software, with a certain

deviation from the actual value. In addition, it is troublesome to adjust the

downtilt angle of a mechanical antenna. The maintenance personnel usually

have to climb to the antenna installation position to adjust the downtilt angle in

the night. What’s more, in some cases, after antennas are installed, it is very

difficult to adjust the downtilt angle, for example, when the antennas are installed

on mountain top, on special buildings, and so on.

WCDMA is very sensitive to interference and noises. If three or more sector

signals with similar level exist in a certain area, pilot pollution will occur and the

cell capacity will decrease. Therefore, in urban areas, during antenna selection,

electricity downtilt antennas are preferred. An electrically controlled antenna is

expensive (twice the price of a non-electrically controlled antenna). Therefore, if

the project is investment sensitive, we should select preset electricity downtilt

antennas in priority.

2.5.2 Comparison between Preset Electricity Downtilt and Zero-Point Filling

We can solve the problem of tower-bottom shadow effect caused by zero-point

by means of preset electricity downtilt or zero-point filling. But the two methods

are different from each other. The use of preset electricity downtilt can shorten

the coverage range of the main lobe, but in occasions where downtilt angles are

generally large, it can expand the downtilt angle adjustment range. Through

zero-point filling, a kind of shaping technology, we can obtain a good pattern. In


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this case, the upper side lobe can be suppressed, so this kind of antennas will

influence other aspects. Certainly it cannot expand the downtilt angle adjustment

range. At present, manufacturers all provide WCDMA NodeB antennas with

zero-point filling and upper side lobe suppression as necessary features.

In wide-coverage occasion, the zero-point depth effect of antennas is a sensitive

point, so we recommend antennas with zero-point filling, without any special

requirement on the upper side lobe suppression.

For urban coverage, a large downtilt angle adjustment range is required, so we

recommend antennas with characteristics of preset electricity downtilt and upper

side lobe suppression, and preferably with the zero-point filling characteristics.

2.5.3 Planning and Optimization of Downtilt Angle

For an omni antenna, we cannot adjust the mechanical downtilt angle, but we

can select preset electricity downtilt angle antennas.

For a directional antenna, in different occasions, requirements for the downtilt

angle adjustment range are different. The downtilt angle planning can be

analyzed based on two occasions: restricted coverage and restricted capacity.

In case of restricted coverage, the downtilt angle should be adjusted, so that the

main lobe can point to the cell border:

arctan hR

θ ⎛ ⎞= ⎜ ⎟⎝ ⎠

(2.1)

In case of restricted capacity, the downtilt angle should be adjusted so that the

upper semi-power point on the vertical side of the main lobe is directed to the cell

border:

arctan2

h V HPBWR

θ −⎛ ⎞= +⎜ ⎟⎝ ⎠

(2.2)

If preset electricity downtilt antenna, we should deduct the electricity downtilt part

when setting the mechanical downtilt angle. If the required downtilt angle is

smaller than the preset electricity downtilt angle, we can obtain the required

downtilt angle by means of mechanical uptilt.

2.6 Principle for Front-to-back Ratio Selection

In occasions where NodeB sites are densely distributed, if the back lobe is too

big, it will be likely to cause pilot pollution and the network quality will be


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influenced. In urban areas, the antenna front-to-back ratio should be ≥ 25dB. In

suburbs or rural areas, the antenna front-to-back ratio can appropriately lower.

The front-to-back ratio is in reverse proportion to the beam width. The narrower

the beam is, the higher the front-to-back ratio is.

2.7 Principle for Antenna Size Selection

Antenna size selection is mainly related to the installability. In areas with

restricted installation conditions, for example, for railway and tunnel coverage

planning, this is a very important factor, or the critical factory that determines

whether the antennas can be installed.

Firstly, the antenna size is related to the technical level of manufacturers, so

different manufacturers can produce antennas of different sizes while all other

indices are the same.

Secondly, the antenna size is related to the antenna gain. The higher the gain is,

the more the dipoles are required, and as a result, the longer the antenna will be.

2.8 Principle for Antenna Impedance Selection

The input impedance of a combiner is 50Ω. In order to reduce the standing wave

ratio, the characteristic impedance of an antenna should match with the input

impedance, namely, it should be 50Ω. In general, the characteristic impedance

can meet this requirement, but attention should be paid to this index during

selection or certification of new antennas.

2.9 Principle for Antenna Selection at Special Occasions

In some cases, the area to be covered around the NodeB can be clearly

distinguished from the areas not to be covered. In this case, we can select

beams matching the landform of such places for coverage. The selection of the

shape of main beam horizontal pattern of an antenna is determined based on the

coverage requirement around NodeB. We can select the pattern according to the

location of the NodeB and the landform of the coverage areas. Namely, the

shape of the antenna beam should match with the landform of the area to be

covered. Common landform-matching beams include 8-figure-shape beam,

heart-shape beam and so on. These antennas all come from omni antennas.

An 8-figure-shape omni reshaped antenna is composed of an ordinary omni

antenna and two auxiliary reflecting metal tubes that are symmetric to each other.

The reflecting metal tubes are used for changing the horizontal pattern of the


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omni antenna by means of coupling so that horizontal pattern is in the shape of

∞. For the “pure” highway coverage (it refers to the coverage of important

highways in non-residential areas), because the traffic is small, O1 type of

NodeBs are commonly used to reduce the quantity of NodeBs and thus save the

construction cost. It can be seen that 8-figure-shape antennas are suitable for

“pure” highway coverage. When this kind of antennas is used, the site location

selection is very important. The stretching direction of the highway should match

as much as possible with the antenna pattern.

Railroad/H

ighway

figure 6 The 8-figure-shape omni antenna pattern (horizontal)

In rural areas, there are many villages by the highway, so village coverage can

be included in highway coverage. We can select heart-shape omni antennas for

this purpose. In the direction of the highway and villages, the antenna gain can

be increased to about 13dBi so that the coverage of the highway and villages is

more efficient.

Highway/Railroad

Highway/Railroad

Village

figure 7 Heart-shape omni antenna pattern (horizontal)


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3 NodeB Antenna Type Selection at Different Scenarios

In a mobile communications network, antenna selection is of great importance.

Antennas should be selected based on the actual situations such as the NodeB

design and network coverage requirements and interference conditions. Properly

selected antennas can improve the coverage effect, reduce interference, and

improve the service quality. Based on the landform and distribution of

subscribers, the application environments of antennas can be classified into

eight types: Urban (a great number of buildings, heavy traffic), suburbs (low

buildings, open area), rural (little traffic), highway (banding coverage),

mountainous areas (hills, sparse subscribers), offshore (extremely far-reaching

coverage, small number of subscribers), tunnels and indoor.

If not otherwise specified, on-site engineers should select antennas within

the range of antennas types already certified in the antenna databasei.

3.1 NodeB Antenna Type Selection for Urban Coverage

Application environment characteristics: NodeBs are densely-distributed, and the

coverage area of each NodeB should be small. Cross-cell coverage should be

avoided to reduce pilot pollution so as to improve the network quality and

expanse the network capacity.

Principle for Antenna Type Selection:

Working frequency

In order to reduce the number of antenna codes, select exclusively wideband

antennas that work at the 1710 ~ 2170 MHz band.

Polarization mode

As it is difficult to select the sites of NodeBs and the installation space of the

antenna is limited in urban areas, so we recommend dual polarization antennas.

Horizontal beam width

In order to better control the coverage range of cells to suppress interference, for

urban 3-sector sites, we recommend directional antennas with 60 ~ 65° horizontal

beam width. When the antenna gain and the horizontal beam width are determined,

the vertical beam width is also determined.

Antenna gain

As large-distance coverage is not required for NodeBs in urban areas, we


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recommend antennas with mid-high gain. Based on the currently available antenna

types, we recommend antennas with 13 ~ 16dBi gain depending on the density of

NodeBs and building structures. Micro cell antennas in urban areas can be of 10 ~

12dBi or lower gain.

Antenna downtilt

Select antennas with 6° electricity downtilt (when the actual downtilt angle is < 6°, it

can be adjusted through mechanical uptilt). Meanwhile, the antenna support should

be mechanically adjustable within the range of 0 ~ 15°. In such a case, there is a

big possibility of capacity expansion. If the cell split mode is adopted for capacity

expansion at late stages, adjustable electricity downtilt antennas can be used. The

antenna downtilt should be adjustable within the range of 0 ~ 10°.

Zero-point filling and upper side lobe suppress

In urban areas, in order to reduce cross-area interference, large downtilt angle is

required sometimes. When the downtilt angle exceeds half of the width of the

vertical beam, we should consider the influence of the upper side lobe. We

recommend antennas with upper side lobe suppression and zero-point filling

characteristics.

Front-to-back ratio

In urban areas, interference control is a key issue, so there is a strict requirement

on the front-to-back ratio of antennas. We recommend antennas with a

front-to-back ratio of 25dB or higher.

Recommendation: Working frequency at 1710 ~ 2170 MHz / ±45° dual

polarization / 65° horizontal beam width / 15 dBi antenna gain / preset 6°

electricity downtilt or 0 ~ 10° adjustable electricity downtilt and 0 ~ 15° adjustable

mechanical downtilt / upper side lobe suppression and zero-point filling / 25dB or

higher front-to-back ratio.

3.2 NodeB Antenna Type Selection for Suburb Coverage

Application environment characteristics: The application environment of the

suburbs is between urban environment and rural environment. In some places,

the environment is more close to the urban, where many NodeBs exist. In this

case, we should consider both coverage and interference control when selecting

the antenna type. In some other areas, the environment is more close to rural

areas, where coverage is an important factor. Therefore, the antenna type

selection should be carried out depending on the actual situations for urban

areas and rural areas.


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Based on the NodeB type design, select antennas with 65° or 90° horizontal beam

width. If NodeBs are densely distributed, the antennas should be selected in

reference to antenna selection principle for urban areas; if NodeBs are sparsely

distributed, and there is no big capacity expansion potential, the antenna selection

principle for rural areas can be used as reference.

Antenna downtilt

In general, preset electricity downtilt antennas are not used. Even if downtilt is used,

the downtilt angle is generally very small.

Recommendation: Select the specific antennas by referring to antenna type

selection for urban areas and that for rural areas depending on the distance

between NodeBs.

3.3 NodeB Antenna Type Selection for Rural Areas

Application environment characteristics: NodeBs are sparsely distributed, the

traffic is low, and large coverage is required. In some places, single NodeB

coverage is adopted. Coverage is the most important factor. Antennas should be

selected depending on the coverage areas around the NodeBs.


Working frequency

In order to reduce the number of antenna codes, select exclusively wideband

antennas that work at the 1710 ~ 2170 MHz band.

Polarization mode

Buildings in rural areas are relatively low and sparsely distributed. The polarization

effect of electric waves is not obvious, so we recommend vertical polarization

antennas.


If a NodeB is required to cover the surrounding area without obvious directionality,

and the traffic is dispersedly distributed around the NodeB, we recommend omni

NodeB coverage. For an omni NodeB, because the antenna gain is small, the

coverage radius is not as far as that of a directional NodeB. If the operator requires

a longer coverage distance, directional antennas should be selected. In rural areas,

we recommend directional antennas with 90° horizontal beam width; for special

landforms, we recommend landform matching antennas.


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Antenna gain

Antenna gain should be selected depending on the coverage requirement. In rural

areas, we recommend omni antennas with 11dBi gain or directional antennas with

18dBi gain.

Antenna downtilt

In rural areas, there is little requirement for downtilt adjustment, both in the

adjustment range and characteristics, so we recommend mechanical downtilt.

Zero-point filling

If the antenna height is over 50 meters and near-end coverage is required, the

antenna must bear the characteristic of zero-point filling.

Recommendation (for directional antennas): Working frequency 1710 ~ 2170

MHz / vertical polarization / 90° horizontal beam width / 18 dBi antenna gain /

without preset downtilt / zero-point filling

Recommendation (for omni antennas): Working frequency 1710 ~ 2170 MHz /

vertical polarization / 11 dBi antenna gain / without preset downtilt / zero-point

filling

3.4 NodeB Antenna Type Selection for Highway Coverage

Application environment characteristics: Low traffic, high-speed moving

subscribers; the key point is coverage. High way coverage is mainly belt-shape

coverage, so dual-sector or 8-figure-shape omni NodeBs are mostly used; in

places where the highway runs through towns or scenic spots, 3-sector or

heart-shape omni NodeBs should be used.


Polarization mode

For highway coverage, we recommend vertical polarization antennas.


For coverage of railroads and highways, in case of S0.5/0.5 NodeB type

configuration, use directional antennas with high gain and 30~33° horizontal beam

width; in case of O1 NodeB type configuration, use 8-figure-shape antennas with

dual 70° horizontal beam width.

For NodeBs used to cover highways and the towns along highways, select

heart-shape antennas or omni antennas with horizontal beam width of 210 ~ 220°.

Antenna gain

In case of directional antennas, select 21 ~ 22dBi high-gain antennas; in case of


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omni antennas, select 11dBi gain antennas; in case of 8-figure-shape antennas,

select 14dBi gain antennas; in case of heart-shape antennas, select 12dBi gain

antennas.

Antenna downtilt

For places where highway coverage is considered mainly, we recommend

antennas without preset downtilt angle.

Zero-point filling

If the antenna elevation is over 50 meters and near-end coverage is required, the

antenna must bear the characteristics of zero-point filling.



without preset downtilt / zero-point filling

Recommendation (for 8-figure-shape antennas): Working frequency 1710 ~

2170 MHz / vertical polarization / dual 70° horizontal beam width / 14 dBi

antenna gain / without preset downtilt / zero-point filling

Recommendation (for heart-shape antennas): Working frequency 1710 ~

2170 MHz / vertical polarization / 210° horizontal beam width / 12 dBi antenna

gain / without preset downtilt / zero-point filling

For highway and railway coverage, we recommend S0.5/0.5 NodeB

configuration with high-gain directional antennas or O1 NodeB with

8-figure-shape antennas to avoid handover of high-speed moving subscribers

under towers.

3.5 NodeB Antenna Type Selection for Rural Coverage

Application environment characteristics: In remote hilly and mountainous areas,

due to serious obstruction of mountains, the propagation attenuation of the

electric wave is rather serious, so it is difficult to cover such as areas. Common

situations are as follows: NodeB sites in basin areas, NodeB sites on high

mountains, NodeB sites at mountainside and NodeB sties in common

mountainous areas. For NodeB sites at the center of a basin area, if the basin

area is not large, we recommend omni antennas; if the basin area is very large

or coverage of a trunk road that runs through the basin is to be considered, we

recommend directional antennas. Restricted by microwave transmission

sometimes, a NodeB site must be located on a rather high hill. In this case, the

antenna will be over 150 meters above subscriber distribution. If the target area

of coverage is near the foot of the hill, an omni antenna with electricity downtilt


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angle is required so that the signal waves will point downward to avoid the

“tower-bottom shadow effect”. In case of a NodeB site at the mountain side, the

antenna elevation is lower than the mountain top, and it is impossible to cover

the other side of the mountain. Therefore, a directional sector antenna with great

beam width should be used to cover the valley.


Polarization mode

For mountainous area coverage, we recommend vertical polarization antennas.


In case of directional antennas, 90° horizontal beam width is recommended.

Antenna gain

In case of omni antennas, 11dBi gain is recommended; in case of directional

antennas, gain of 15 ~ 18dBi is recommended.

Antenna downtilt and zero-point filling

For NodeB sites on the mountains while the place to be covered is down at the foot

of the mountains, antennas with the zero-point filling and preset electricity downtilt

characteristics are recommended. The preset downtilt angle depends on the

relative height of the antenna elevation compared with the altitude of the coverage

area. The bigger the antenna relatively height is, the bigger the preset angle should

be.



preset electricity downtilt / zero-point filling


vertical polarization / 11 dBi antenna gain / preset electricity downtilt / zero-point

filling

3.6 NodeB Antenna Type Selection for Offshore Coverage

Application environment characteristics: Low traffic, wide coverage, good radio

propagation environment; for offshore coverage, the coverage distance is mainly

restricted by the sphere curvature of the earth and the radio propagation

attenuation. In view of the influences of the sphere curvature of the earth,

antennas are usually installed at a high elevation (over 100 meters) for sea

surface coverage.



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Polarization mode

For offshore coverage, we recommend vertical polarization antennas.


We do not recommend omni antennas. The horizontal beam width of directional

antennas should be selected depending on the coverage requirements.

Antenna gain

Because the required coverage radius is big, we recommend high-gain (over 18dBi)

antennas.

Preset downtilt and zero-point filling

For sea surface coverage, the antenna elevation is usually very high (over 100

meters). Therefore coverage holes are like to appear at the near end. We

recommend antennas with the zero-point filling characteristic. Meanwhile, for

long-distance and wide coverage, we recommend antennas without preset downtilt.

Recommendation: Working frequency 1710 ~ 2170 MHz / vertical polarization /

30° horizontal beam width / 21 dBi / without preset downtilt / zero-point filling

3.7 NodeB Antenna Type Selection for Tunnel Coverage

Application environment characteristics: The traffic is not heavy, and interference

control is almost not required. As it is rather difficult to install and maintain

antennas inside tunnels, the large-sized antennas are not adopted in most cases.

Leaking cables will be adopted for railroad tunnel coverage, which will not be

discussed in this section.

Principle of Antenna Type Selection:

Polarization mode

Because the inner wall of tunnels and vehicles can repeatedly reflect signals,

causing obvious polarization effect on electric waves, the coverage capability of a

vertical polarization antenna is similar to that of a ±45° polarization antenna in a

tunnel. For installation inside tunnels, the antenna size and installability should be

considered. We recommend vertical polarization log-periodical antennas (wideband)

or Yagi antennas (narrowband). For installation outside the tunnel entrance, we

recommend dual polarization plate antennas.


Due to obvious coverage directivity, narrow-beam directional antennas are usually

used. The log-periodical antennas or Yagi antennas with 55° horizontal beam width

or plate antennas with 30° horizontal beam width are recommended.


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Antenna gain

We can select high-gain plate antennas (21dBi or higher), Yagi antennas

(13~14dBi) and log-periodical antennas (11 ~ 12dBi). The specific antenna gain

can be selected based on the tunnel length.

Antenna size

For tunnel coverage, the antenna size is a critical factor. A special coverage

scheme should be designed for each tunnel, and antenna installability should be

given due consideration. Select small-sized and easy-to-install antennas those

meet the gain requirement.

Recommendation: Working frequency 800 ~ 2200 MHz / vertical polarization /

55° horizontal beam width / log-periodical antenna with 11.5 dBi (consider

sharing with GSM/DCS).

3.8 NodeB Antenna Type Selection for Indoor Coverage

Application environment characteristics: At low stories of high buildings, NodeB

signals are usually weak and there are even coverage-hole zones; at high stories

of high buildings, signals are in disorder, interference is serious and the call

quality is bad. Most of underground facilities, like underground parking lots and

underground stores, are coverage-hole zones.

Generally, indoor distribution systems are built to solve indoor coverage

problems. With an indoor distribution system, NodeB signals are directly led in

for various indoor areas through a wired network, and then the signal receiving

and transmission are implemented through various indoor antennas, so as to

remove indoor coverage-hole zones, suppress interference and provide good

coverage for indoor subscribers.

There is no receiving diversity or transmission diversity in an indoor distribution

system. The antenna type selection depends on the design of the distributed

system. Check the installability of the antennas and the coverage requirement,

and select accordingly the antenna type and parameters.


Working frequency

In general, indoor distribution systems all involve antenna sharing

requirement, so the compatibility with forward (GSM/DCS) and backward

(WLAN) should be considered in antenna selection. Therefore the antennas

for indoor distribution systems should be wideband antennas (800 ~ 2500

MHz).For Green Field operators like China Telecom, wideband antennas


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are also recommended. An important reason is that DCS bands after

clearing may be adopted in new mobile communications modes in the

future.

Polarization mode

Vertical polarization mode is adopted for indoor coverage.

Antenna type selection

Indoor antennas come in three types: ceiling-mounted omni antennas, plate

directional antennas, and high-gain directional antenna.

An omni antenna is installed in ceiling mounted mode at the center of the

room; a plate directional antenna, applied in a rectangle environment, is

installed on a single-sided wall by the short edge of the rectangle; a

high-gain directional antenna is applied in the elevator well, and in general it

is a log-periodical antenna.

Antenna gain

Omni antenna: 2dBi; plate directional antenna: 7dBi; log-periodical

directional antenna: 11dBi.

Beam width

Omni antenna: 360° horizontal beam width and 90° vertical beam width;

plate directional antenna: 90° horizontal beam width and 60° vertical beam

width; log-periodical antenna: 55° horizontal beam width and 50° vertical

beam width.

Plate antenna unit: Different sizes are available, used in elevator pass ways,

tunnels, subways and corridors respectively.


vertical polarization / 360° horizontal beam width, 90° vertical beam width / 2dBi

gain.

Recommendation (for plate directional antennas): Working frequency 800 ~

2500 MHz / vertical polarization / 90°horizontal beam width, 60° vertical beam

width / 7dBi gain.

Recommendation (for log-periodical antennas): Working frequency 800 ~

2500 MHz / vertical polarization / 55°horizontal beam width, 50° vertical beam

width / 11.5dBi gain.


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List of references:

[1] Jiang Lihong, WCDMA Antenna Database, RF Research Department of Shanghai Research

Institute, 06/2003

[2] Jiang Lihong, WCDMA NodeB Antenna Type Selection in Urban Areas, RF Research

Department of Shanghai Research Institute, 11/2002

[3] Jiang Lihong, WCDMA NodeB Antenna Type Selection in Villages and Suburbs, RF

Research Department of Shanghai Research Institute, 12/2002

[4] Jiang Lihong, WCDMA NodeB Antenna Type Selection in Highways, RF Research

Department of Shanghai Research Institute, 01/2003

[5] Jiang Lihong, WCDMA NodeB Antenna Type Selection of Indoor Distribute System, RF

Research Department of Shanghai Research Institute, 01/2003

[6] Ding Jianmu, WCDMA RNP Technologies Influences of Antenna Mechanical Downtilt on

Capacity, Adjacent Cell Interference and SHO Overhead, UMTS Network Planning

Department, 04/2003

[7] Tao Maodi, He Qun, GSM NodeB Antenna Type Selection Guideline, GSM Network

Planning, 01/2002

Documents

WCDMA RNP Antenna Type Selection Guidance-20040716-A-1.0