30508788 Antenna Knowledge

7/30/2019 30508788 Antenna Knowledge

1/22

Antennas in network optimization

1. The application of antenna parameters to the system planning for

mobile communication.

1) Radiation pattern

(1) horizontal pattern has to do with beam width and coverage area.

(2) the beam width in vertical pattern determines the power distribution over

coverage.


2/22

2)Communication Distance FormulaPT(dB)=PR(dB)+20log4R(m)/min(m)-GT(dBi)-GR(dBi)-Lc(dB)-L0(dB)

In the equation, Lc stands for the loss of the feeder cable for BTS

antennas; L0 the wave loss during propagation.

In system designing, a margin should be reserved for L0. In general,wave propagation loss has a bearing on the environmental condition

during propagation. For example, radio waves suffer a loss of 10-15dB, upon penetrating civil construction or trees; 25-30dB in thecase of concrete walls.

As for mobile phones in CDMA /GSM of 800MHz or 900MHz, it isgenerally believed that the receiving threshold is1.4dBm. But

actually, the received signal should be 10dB higher than this value, sothat the received signal can reach the standard in signal-to-noise ratio.As a matter of face,receiving power is taken as170dBm in calculating,so as to guarantee good telecommunication.


3/22

A BTS is supposed to features the following constants:

Transmitting power PR=-70dBm

Receiving power PT=20w=43dBm

Cable lossLc=2.4dB(60

The gain of the receiving antenna Gr=1.5dBi

Operating wave length =33.333cm(f0=900MHz)

43dBm-(-70dBm)+GT+1.5dBm=32dB+20logR(m)+2.4dB+L0Substituting the above values yields 80.1dB +G

T(dBi )=20logR(m)+ L0

It is believed that good communication can be maintained when GT

(dBi )>20logR(m) -80.1dB + L0.


4/22

If the BTS adopt omni-directional antenna ofGT

11dBi, goodcommunication will be ensured within 1km whenL

0


5/22

.

S

40m

S

S

18o

In the case of vertical beam shown in the diagram, GT

in the above

calculation refers to the value on the main axis. Usually installed on the

tower, the BTS antenna should be titled to guarantee enough power coverage

for the receiver. The title angle is determined by the height of tower and the

distance between the user and the antenna


6/22

As seen in the above vertical pattern, shadow under the tower will

result if the receiver happens to stand in the null-coverage of the beam.

To combat this problem,null-fill antenna can be adopted. The

alternative solution is to downtilt the beam.

2. Antennas in network optimization

1) the definition of network optimization

It refers to the proper adjustment of regulation and design of the

communication network according to certain guidance so as to ensure

reliability and cost efficiency of the network. It aims at betteroperation quality and high utilization ratio of radio resources, all of

which is essential for both mobile user and operator.


7/22

2. Main content of network optimization

Based upon the above discussions, we can summarize thenetwork optimization having the following content:

(1)Efforts should be made to realize 90% of seamlesscoverage, non shadow area,and min receiving electriclevel in the radiation area.

(2) Rationalize the configuration of ratio resources, increasefrequency reutilization ratio, and expand network capacity.

(3)Reduce interference and call-drop rate,and increase call-

completing ratio.All these have to do with the proper selection and

adjustment of BTS antenna parameters.


8/22

The function of antennas in network optimization

1) To realize seamless coverage, the proper selection of

BTS antenna parameters is of essential importance.As

for GSM or CDMA BTS for digital mobile

communication network, the selection of BTS antennasavailable at home is based upon the following principle:

Tilt angle can be reached by the following formula:

arc h/ r/2

(in which stands for tilt angle;h height of antenna, r thedistance between base stations.


9/22

(a) In high-volume areas, the distance between stations is 300-500m, and the

title angle should be 10-19o. To satisfy these needs, we suggest a45dual

polarized directional antenna with inbuilt 9o electrical downtilt and

65obeam width. Working with mechanical downtilt mounting kits of 15o,

the antenna secure that the pattern in horizontal directional remain constant

when the main beam tilts 10-19o. The wide application of the antenna

indicates that it can satisfy coverage need in high density urban areas .

(b) In medium-volume urban areas,the distance between stations is bigger than

500m and downtilt angle should be 6-16o. In this case,45dual

polarizeddirectional antenna with inbuilt 6o electrical downtilt and

65o

beam width can secure consistent half power beam width when themain beam tilts 6-16o ,and satisfy coverage need in medium density urban

areas .

(c) In low-volume urban areas, the distance between stations are large and the

tilt angle should be 3-15.


10/22

In this case,45dual polarized directional antenna with inbuilt 3o

electrical downtilt and 65obeam width can secure consistent half power

beam width when the main beam tilts 3-15o ,and satisfy coverage need in

low density urban areas .

2) Antenna selection for small town areas:

In these low volume areas, the main consideration should be paid to

coverage need,hence large distance between stations feasible. In this case,

we can select single polarized antennas(triple or dual section) featured by

higher gains(17dBi) and larger horizontal beam width(65,90).


11/22

3) Antenna selection for the countryside

In these low volume areas, coverage need is the first consideration. So a

good choice is omni-directional high gain antennas with 3,5,7 tiltangle.

4) Antenna selection for highways/railroads and nearby towns(1) Dual section (180for each) . This design features 90half power

beamwidth and high gain(17-18dBi) antennas and back-to-back installation

with the largest radiating directed along highway. Their resultant radiation

pattern is shown in the below diagram.


12/22

(2) High-way dual-directional antenna. If the volume is rather small along

highway/railway, we can select dual polarized antennas, a modification

of omni-directional antenna, featured by 70beamwidth and 14dBi

gain. Its pattern is shown as follows.

Railway andhighway


13/22

(4) Highway&town antennas:In the low-volume areas where both

highway/railway and nearby town should be covered, weak directional

antenna is used to satisfy the coverage need.

(5) radiation-controlled pattern

Highway;railway

town

Highway;railway


14/22

(1) Horizontal beam

High front-to-back ratio

Side lobe suppression across frequency band

Remain constant 10dB beamwidth of horizontal beam during the adjustment oftilt angle.

(2) vertical beam

Side lobe suppression across frequency band

Null fill feature

Consistent gain across frequency band.

Dual polarized antennas should feature enough isolation and space

polarization discrimination.6) Increase carrier-to-signal ratio by the adjustment of BTS antennas.

7) Improve the speech quality in coverage area , balance the network load, andimprove network operating efficiency by the adjustment of BTS antennaselevation angle.


15/22

Adjustment of antennas in network

adjustment of tilt angle

No tilt Electrical tilt Mechanical tilt

Antennas are tilted to direct the beam to the ground.


16/22

Beam down tilt

Intended for:

coverage control

reduction of IM

Two methodsMechanical

Electrical


17/22

Beam coverage in the case of electrical tilt

Electrical tiltNo tilt


18/22

Beam coverage in the case of

mechanical down tilt

No tilt Mechanical tilt


19/22

Comparison between two methods

10electrical down tilt 6

electrical down tilt+4mechanical tilt

10mechanical tilt


20/22

How to realize adjustable electrical downtilt


21/22

the realization of electrical down tilt

No tiltFeeding lines of the same length

Tilt

Feeding lines of different length


22/22

To adopt the electrical tilt function, it has

fixed electrical tilt products and

continuous tilt adjustment products. Forthe continuous tilt adjustment products,

they can be adjusted directly at the bottom

of the antenna or be adjusted through a

control unit remotely.

Documents

30508788 Antenna Knowledge