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 6
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
good results when fieldstrength in the horizon is reduced by about 6 dB
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 Horizontal pattern 105° / mechanical DT
more elegant is the electrical downtilt with the antenna remaining upright; instead of equal phases on the dipoles, perticular phase distributions are selected by varying the cable lengths to the dipoles
adjustability of the mechanical DT + technical advantage of the electrical DT results in adjustable electrical DT
phase shifters at each dipole provide a variable phase distribution Ф Ф
Ф Ф
for sidelobe control the dipoles are fed with different power max. electrical DT angle approx. 14° (for higher DT angle a combination of mechanical and electrical DT is recommended
Maximum Electrical Downtilt Angle Antenna Type 742 212 / Xpol F-Panel 1710-2170 65° 18dBi 0°-8°T
Vertical pattern example at 0°T (polar-logarithmic scale)
Vertical pattern example at 8°T (polar-logarithmic scale)
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. 15
In general: Adjustable electrical downtilt is normally used for coverage fine tuning.
In special cases, i.e. antenna mounting on high rise buildings or in special test scenarios, a higher downtilt angle could be stipulated.
In this cases, an acceptable compromise is to combine electrical and mechanical DT mechanical downtilt kit : primary downtilting adjustable electrical downtilt : fine tuning
