- This topic has 5 replies, 1 voice, and was last updated 14 years, 4 months ago by kulafifu.
17th October 2006 at 12:07 #45938kulafifuGuest
just curious. why is there a need to observe separation between a GSM and a WCDMA antenna? If the reason is some sort of intermod or interference, why can’t there be no such problem in a WCDMA/GSM combiner? thanks17th October 2006 at 12:11 #45939kulafifuGuest
what is the difference between electrical downtilt and mechanical downtilt? and why is there a need to downtilt an antenna? what are the important antenna parameters that affect the overall performance of a cellular system. thanks17th October 2006 at 18:10 #45940PixGuest
mechanical downtilt : the whole antenna is tilted downwards.
electrical downtilt : the antenna is straight but the radio pattern is tilted, thanks to adjustment of antennas inner elements.
you need to downtilt an antenna because otherwise it is shooting straight, meaning half the beam is going over the horizon (propagating very far, creating interferences). And also, without a tilt, at the bottom of the antenna tower you might have a low signal strength (true if antenna is located high and there are not many buildings around (no reflections)).
Important parameters : half power beam width (from 60° to 260°), the vertical h.p.b.w. (from 15° to 3°), the gain (from 2dBi to 22dBi), the front-to-back ratio and of course, the electrical tilt..
for urban design, start with antennas with following characteristics : HPBW 65°, V-HPBW =7°, (gain should be about 18dBi), electrical downtilt = 6°.
good luck…18th October 2006 at 01:35 #45941kulafifuGuest
thanks pix. how about an answer to the other question? again, thanks19th October 2006 at 05:49 #45942PixGuest
i’m not so familiar about the intermodulation problems. If i had to plan a GSM site + a UMTS site, I would simply read the recommendations and apply them. If the vendor says there is no problem in the combiner, I trust him 🙂
The decoupling in the combiner is very high, while the “Air” decoupling increases with distance between antennas.25th October 2006 at 01:40 #45943kulafifuGuest
i would like to know the meaning of sidelobe supression and null fill. thanks