4-Antenna Principle and Model Selection-58

WCDMA Antenna Principle and Modelselection

ZTE University

TD&W&PCS BSS Course Team

Objectives

At the end of this course, you will be able to: Grasp Signification of Antenna Technical

Parameters.

Grasp Antenna Model Selection

Content

Principles of Antenna

Model Selection of Antenna

Principles of Antenna (1)

n What is antenna? Antenna converts the electrical signals from the conductive wire

into radio wave and transmits it into the air Antenna collects the radio wave and converts it into electrical

signals

Blah blahblah bl ah



n When the conductive wire has alternating current, it can form radiation

of electromagnetic wave, with the radioactive capacity related to the

length and form of the conductive wire.

n When the length of the conductive wire increases to a degree

comparable to wavelength, the current on the conductive wire sharply

increases, forming strong radiation. Generally the straight conductive

wire above that can form noticeable radiation is called dipole .



n A dipole with the two rods of the same length is called

symmetrical dipole, or 1/2 wavelength dipole. A single 1/2

wavelength symmetrical dipole can be used independently, or

multiple 1/2 wavelength symmetrical dipole can form an antenna

array.

Wavelength

1/2 Wavelength1/4 Wavelength

1/4 Wavelength

1/2 Wavelength

dipole


Outer View of Antenna (1)

n --- Outdoor NodeB patch directional antenna


Outer View of Antenna (2)

Indoor ceiling-mount antenna Indoor wall-mount antenna

--- Indoor antenna


For example, 1 symmetrical dipoleReceiving power: 1mW

Antenna array of 4 symmetrical dipolesReceiving power: 4 mW

GAIN= 10log(4mW/1mW) = 6dBd

The high gain of the patch antenna is formed by the antenna array of multiplebasic dipoles

Gain of Antenna


Gain of Antenna

n The definition of the gain of an antenna is related to the 1/2wavelength dipole or the omni radiator.

n The omni radiator assumes that the radiation powers in all directionsare equal. The gain of the antenna in a certain direction is a value ofthe field strength generated in this direction over the intensity by theomni radiator in this direction.

n Generally the gain of the antenna has two units: dBd and dBi.

n dBi indicates the field strength in the direction of the largest radiationof the antenna, compared with the reference value of the omni radiator.

n The gain of the antenna compared with the 1/2 wavelength dipole isindicated with dBd.

n 0dBd=2.15 dBi


Difference of dBd and dBi

2.15dB

Pattern radiation of asingle symmetrical dipole

A omni homogeneousradiator has the same

radiation in all directions

Gain of an antenna compared with asymmetrical dipole is indicated with dBd.Gain of an antenna compared with an omnihomogeneous radiator is indicated with dBi.For example: 3dBd = 5.15dBi


Antenna Direction (1)

n The antenna direction refers to the capability of radiating

electromagnetic wave in a certain direction.

n For the receiving antenna, pattern means the receiving

capability of the wave promulgated from different

directions.

n The characteristic curve of antenna direction is usually

indicated with pattern.

n Pattern is employed to describe the capability of

transmitting/receiving electromagnetic wave in all

directions in the space.


Antenna Pattern (2)

Top view


120(eg)

Peak

- 10dB point

- 10dB point

60 (eg) Peak

- 3dB point

- 3dB point

15 (eg) Peak

Peak - 3dB

Peak - 3dB

32 (eg) Peak

Peak - 10dB

Peak - 10dB

Vertical pattern

3dB beamwidth Horizontal pattern 10dB beamwidth

Beamwidth of Antenna


Horizontal Lobe 3dB Width


Directional antenna Omni antenna

Vertical Lobe 3dB Width


Work Frequency Range of Antenna

n In disregard of transmitting or receiving antenna, it alwaysworks within a certain frequency range. With the considerationsof out-of-band anti-interference capacity, the usual practice is toselect the bandwidth of the antenna that just meets thefrequency requirements.

At 850MHz, the 1/2wavelength is best

At890

MHz Antennadipole

At820

MHz


Polarization of Antenna

n The field direction of the electromagnetic field of the antenna radiation is thepolarization of the antenna. The NodeB antenna usually applies linearpolarization. With the ground as reference plane, if the field vector isperpendicular to the ground, it is vertical polarization (VP); if the field vector isparallel to the ground, it is horizontal polarization (HP). In the case of a dual-polarization antenna, the +45 and -45 orthogonal dual-linear polarization areadopted.

Verticalpolarization

Horizontalpolarization

+ 45 tilted polarization - 45 tiltedpolarization


Dual-polarization Antenna

n The dual-polarization consists of two antennae with orthogonal poles

within the same radome. The adoption of dual-polarization antenna can

sharply reduce the number of antennae, streamline the installation

engineering of antenna, lower cost, and save space in antenna

installation.

V/H(vertical/horizontal) Tilt (+/- 45)


Antenna Beam Downtilt

n Applied to suppress coverage and reduce cross-

modulation

n Two modes: Mechanical downtilt and electrical downtilt


Impact of Downtilt on Coverage


Beam Downtilt

n The purpose of the downtilt technology is to tilt the main beam to

reduce the radiation level to the adjacent coverage cells. In the case,

though the frequency level at the edge of the cell is reduced, the

interference level is much lower than the frequency level.

No downtilt ElectricaldowntiltMechanical

downtilt


Phase Shifter

Principle of Electrical Downtilt


Electrical Downtilt and Mechanical Downtilt


F/R Ratio

n In the antenna pattern, the ratio of max. value of front and back

lobes is called front/back ratio . The F/R ratio of the outdoor

NodeB antenna is preferably generally larger than 25dB.

Front powerRear power


Input Impedance of Antenna

n The ratio of the signal voltage and the signal current of the

antenna and the feeder connection points, or the two ends of

the feeding points, is called impedance of antenna.

n Input impedance has resistance component and reactance

component. For any antenna, we make adjustment through the

antenna impedance. Within the required work frequency range,

the real part of impedance is very small and imaginary part is

very close to 50 W, so that the antenna impedance is Zin = Rin= 50 W. This is necessary to ensure the impedance of antennaand that of feeder to be well matched.


VSWR

n The generation of VSWR : As the incident wave power is transmitted

to the antenna input end and is not completely absorbed (radiation.

Reflection wave is generated and stacked to generate VSWR.

n The value of VSWR is between 1 and infinite. VSWR is 1, indicating

full match. VSWR is infinite, indicating full reflection and full mismatch.

9.5 W80ohms

50 ohmsForward: 10W

Backward: 0.5W


Reflection coefficient :

|G|=|(Za-Zo)/(Za+Zo)|Za: Input impedanceZo: Antenna standard input impedance VSWR=(1+|G|)/(1-|G|).

RL=-20lg|G|,

eg:

if VSWR=1.5:1, then RL=-13.98dB.

VSWR

Side Lobe Suppression and Null Fill-in


Content



Parameters Related to Antenna Model Selection

n In selecting antennae, a large number of antennae is

involved.

n Such parameters as radiation pattern, gain, horizontal

lobe width, vertical lobe width, and downtilt mode are

selected according to the terrain, ground objects, height

of NodeB, and coverage radius in the coverage.

n The selection of other parameters is relatively simple and

done according to the designed system.


Polarization Mode (1)

n NodeB antenna adopts linear polarization mode.

n In particular, single-polarization antenna adopts vertical

linear polarization, whereas dual-polarization antenna

adopts 45 dual-linear polarization.


Polarization Mode (2)

n In downtown of cities, the number of

NodeB is large, and the coverage radius of

each NodeB is small. It is suggested to

adopt dual-polarization antenna.

n In suburb and countryside, the number of

NodeB is small and the coverage radius is

large relatively. Space diversity can be

adopted to enhance the receiving effect of

the NodeB. The single-polarization

antenna can be adopted.


Antenna Radiation Direction

n For an omni antenna, the radiation intensity in

all directions on the same horizontal plane is

equal in theory. It is applicable to the omni cell.

The selection of omni antenna to achieve

large-scope coverage in the countryside is

economical

n The directional antenna enables the direction

of the radiation of the antenna in the horizontal

plane. It is applicable for the coverage of

sector cell. Directional antenna can be

selected for downtown and suburb of cities.


Horizontal Lobe Width

n The horizontal lobe width of the omni antenna is all 360.n In the cases of 20 and 30 widths, the gain is high. They are

applied for the coverage of the narrow land stripes or expresshighways.

n In the case of 65 width, it is applied mostly in the typical three-sector NodeB configuration in the densely populated city areas.

n In the case of 95 width, it is applied mostly in the typical three-sector NodeB configuration in the suburban areas.

n In the case of 105 width, it is applied mostly in the typical three-sector NodeB configuration in the sparsely populated areas.



n Downtown of cities

Suggestions for different scenarios:


n Downtown of cities

The S111 NodeB in downtown of cities generally adopts

antennae with 65 horizontal lob width and 7 to 10vertical lobe width, with the gain of the antennae ranging

within 15 to 18 dBi. For the S110 or directional single-

sector station, the antennae with 65 , 90 or widerhorizontal lobe width. The selection is based on the actual

situation. The selection of vertical lobe and gain is the

same as the S111 station. For omni station, antennae with

small gain and electronic downtilt are selected.



n Suburb and countryside



n Suburb and countryside

Directional antennae adopt antennae with 90 horizontallobe width and 5 to 7 vertical lobe width, with the gainranging within 15 to 18 dBi. Omni antennae adopts

antennae with 5 to 7 vertical lobe width, with the gainranging within 9 to 12 dBi.



n Water surface


n Water surface (large lake and sea surface), gobi, and desert

Directional antenna: If the coverage is relatively open and wide,

antennae with 90 or 105 horizontal lobe width and 5 to 7 , withthe gain ranging within 14 to 18dBi ,vertical lobe width can be

selected. If the coverage distance is long but the width is narrow

(e.g., lake and terrain factors), the 65 narrow beamwidth antennacan be selected.

Omni antenna: The antennae with 5 to 7 vertical lobe width andgain ranging within 9 to 12dBi can be selected



n Narrow land strips



n Narrow land strips (such as highway and railway)

Antennae for highway and railway are selected according to

the coverage line distance and shape of the highway and

railway concerned.

If the line is relatively straightforward, high-gain antennae

with 20 to 30 horizontal lobe width and 5 to 7 vertical lobewidth can be selected.

If the line is a curve in a large amplitude, antennae with 65,90, or even larger horizontal lobe width, and with 5 to 7vertical lobe width can be selected.



n Complicated terrain with

a large fall



n Areas of a complicated terrain with a large fall

n In the actual networking planning, there may be a scenario that

features a large fall. In that case, antennae with 10 to 18vertical lobe width can be selected according to the actual

situation. In another case, the area that needs a large coverage

is higher than the mount height of the antennae. The antennae

with 18 to 30 vertical lobe width can be selected according tothe actual situation.


Downtilt Mode of Antennae (1)

n In the case of mechanical downtilt antenna, it is tilted when they are installed.The price is low. It is mostly applied in the scenario with the downtilt anglesmaller than 10.

n In the case of electrical downtilt antenna, the price is relatively high, yet with alarger downtilt range (larger than 10. When the downtilt angle is wide, theantenna pattern shows no obvious distortion, and the back lobe of the antennawill also be downtilted at the same time.

n In particular, the fixed electrical downtilt antenna with a small angle plus themechanical downtilt scheme has advantages in performance and cost, which isthe mainstream option of downtilt.

Antenna downtilt modes fall into mechanical downtilt and electrical downtilt.Electrical downtilt can be further divided into fixed electrical downtilt andadjustable electrical downtilt.


Downtilt Mode of Antennae (2)

n The application of electrical downtilt antenna includes the followingscenarios: In the case of city sites with specially small coverage radius, large downtilt

angle is needed to reduce the interference with the adjacent cells. In the case of high sites, to reduce the interference with the adjacent cells

and the problem of light shadow, it is better to select the first upper sidelobe suppression and the first null fill-in, with large-angle electrical downtiltor adjustable electrical downtilt antenna.

In the case of sites higher than the surroundings (e.g., mountain top andriverside), electrical downtilt antenna can be selected.

Omni antenna cannot be mechanically downtilted. High omni NodeB shouldselect the electrical downtilt antenna with different angles according to thedifferent situations.


Down tilt angle of Antennae (1)

In downtown area

n a: mechanical down tilt ; H: effective height;

n L: cell radius; b :Vertical Lobe 3dB Width ;

n ge: electrical down tilt;

a = arctg(H/L) + b/2 ge


Down tilt angle of Antennae (2)

a = arctg(H/L) ge

n In rural area

n a: mechanical down tilt ; H: effective height;

n L: cell radius; b :Vertical Lobe 3dB Width ;

n ge: electrical down tilt;


Examples of Antennae (1)

Type: Outdoor omni antennaAntenna manufacturer: KATHREINModel: HXS-201-60-1.9-6-2GHz-60Work frequency: 1920 MHz ~ 2170MHZGain: 11.6 dBiHorizontal 3dB beamwidth: 360Polarization: VerticalAngle: 0Input impedance: 50 WDimensions: f60 1500mmWeight: 3.8kg

Applicable scenario: Suburb and countryside



Type: Outdoor directional antennaAntenna manufacturer: KATHREINModel: TDJS-2000-18-H65-3GWork frequency: 1920 MHz ~ 2170MHZGain: 18dBiHorizontal 3dB beamwidth: 65Polarization: 45 polarizationAngle: 0 ~ 15Input impedance: 50 WDimensions: 1300mm 160mm 75mmWeight: 4.5kg

Applicable scenario: High-density downtownand resident areas



Type: Indoor directional antennaAntenna manufacturer: Mobile Antenna Technologies (Shenzhen)Model: MB5F-70/40-9/6-WWork frequency: 1710 MHz ~ 2170MHZGain: 6 dBiHorizontal 3dB beamwidth: 40Polarization: VerticalAngle: 0Input impedance: 50 WDimensions: 240 220 65mmWeight: 1.5kg

Applicable scenario: Interior of buildings


Beautified antennae



Electrical down tilt antennae

Indoor antennae


Leaky cable


4-Antenna Principle and Model Selection-58

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Transcript of 4-Antenna Principle and Model Selection-58