2 HPBW - Downtilt

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©Kathrein/Scholz 07/02

Network Design

Network configuration

Cell coverageComparison of half power beam widths

Vertical downtiltMechanical downtiltElectrical downtiltAdjustable electrical downtilt

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DownlinkConnection

UplinkConnection

Base Station

Mobile StationBase StationEquipment

RadioLink

Antenna System

Network Design / Base station

Downlink frequencies :

GSM 900 : 935 - 960 MHz

GSM 1800 : 1805 - 1880 MHz

Uplink frequencies :

GSM 900 : 890 - 915 MHz

GSM 1800 : 1710 - 1785 MHz

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Network Design / Configuration

honeycomb structureomni base stations using omni-directional antennas for low traffic cellssector sites with 3 cells (directional antennas) of different frequencies for a higher amount of subscriberssmaller cells (micro cells, pico cells) in high traffic areas (cities, city centers) the topography, the repeatability of the frequencies and the real base station locations influence the network planning

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Cell coverage

To avoid interferences to adjacent cells the target is to provide coverage just for the concerning sector but not beyond the sector border

tools for cell matchinghalf power beam widthtilt of the vertical pattern

Network Design / Cell Coverage

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Network Design / Half Power Beam Width

Which half power beam width is needed to cover a 120° sector ?

standard comparison indicates significant differences at the sector borders

65°90°105°120°

mistake : gain variation is not considered

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antennas with the same vertical length but different horizontal half power beam width differ in the overall gain value

example : 900 MHz / 1.3m length65° 15.5 dBi90° 14.0 dBi105° 13.5 dBi 120° 13.0 dBi

result : no significant difference between 90°, 105° and 120° regarding half power beam width and overlapping area to the adjacent cell

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Conclusion :

the range of half power beam widths can be limited to 65° and 90°

field of application :

urban areas : 65°Theoretically the overlapping area between the cells is too small. But due to reflections from the surrounding the half power beam width is increased.

rural areas : 90° (65°) Reflection intensity is much lower. Therefore many network planners prefer 90° to provide sufficient overlapping. But also 65° is used


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as a standard the vertical beam is pointing to the horizon

downtilting of the pattern provides the following benefits :- the majority of the radiated power is concentrated within the sector - the reduction of the power towards the horizon avoids interference problems

with the next sector

best results when fieldstrength in the horizon is reduced by about 6 dB

Network Design / Vertical Downtilt

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Network Design / Mechanical Downtilt

a mechanical downtilt kit increases the upper distance to the mast and makes the antenna pointing downthe requested downtilt angle is achieved only in main directionat +/- 90° from the main direction the downtilt angle is always zero (rotation axis)effective downtilt varies across the azimuth

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Network Design / Mechanical Downtilt

Horizontal pattern 105° / mechanical DT

Mechanical Downtilt 0° 6°8° 10°effect on the horizontal pattern at the horizon :

reduction of the fieldstrength in main direction without any change +/- 90° to it results in deformation of the horizontal pattern this effect of changing half power beam width can hardly be considered in the network planning and reduces the prediction accuracy

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more elegant is the electrical downtilt with the antenna remaining upright;instead of equal phases on the dipoles, perticular phase distributions areselected by varying the cable lengths to the dipoles

Network Design / Electrical Downtilt

12° downtilt

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Network Design / Electrical Downtilt

Electrical Downtilt :0° 6°8° 10°the fixed phase distribution applies to all azimuth directions ⇒ electrical downtilt angle is constantthe shape of the horizontal pattern remains constantaccurate network planning is assured

Horizontal pattern 105° / electrical DT

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maximum flexibility is achieved with adjustable electrical downtilt by combining the adjustability of the mechanical DT and the technical advantage of the electrical DT

Network Design / Adjust. Electrical DT

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Network Design / Adjust. Electrical DT

phase shifters at each dipole provide variable phase distributionsfor sidelobe control the dipoles are fed with different powermax. electrical DT angle approx. 14°for higher DT angle a combination of mechanical and electrical DT is recommended

adjusting mechanism with scale

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Antenna Type 741 988Xpol F-Panel 1710-2170 88° 14dBi 0°-10°T

Vertical pattern example at 9°T(polar-logarithmic scale)


Downtilt Angle versus Vertical Half Power Beam Width

A greater vertical half power beam width means a higher downtilt angle in order to receive similar results.

Antenna Type 741 990Xpol F-Panel 1710-2170 88° 18dBi 0°-6°T

9°3°

The selected downtilt angle is linked to the respective vertical half power beam width.

6dB point

6dB point

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Antenna Type 742 212 / Xpol F-Panel 1710-2170 65° 18dBi 0°-8°T



Max. power reduction towards the horizon is achieved with the first null.

A higher downtilt angle increases the power again due to the first upper sidelobe.

Maximum Electrical Downtilt Angle

Max. DT angle is determined by the angle between the mainlobe and the first sidelobe .

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Special Cases

In special cases,

i.e. antenna mounting on high rise buildings or in special test scenarios,

a higher downtilt angle could be stipulated.

In general:Adjustable electrical downtilt is normally used for coverage fine tuning.

In this cases,an acceptable compromise is to combine electrical and mechanical DT

mechanical downtilt kit : primary downtilting

adjustable electrical downtilt : fine tuning

Documents

2 HPBW - Downtilt