- This topic has 71 replies, 1 voice, and was last updated 5 years, 6 months ago by Bijoy.
12th February 2008 at 06:18 #50828Huawei RFGuest
I thought in making a small contest between us here…
I will ask a question, and any one knows the answers puts it here… the one who has the first correct answer can put a question. The questioner will decide if it is correct…
I hope you can enjoy it… it will also stimulate you to search inside documents and activate competency spirit…
the first question is:
– How much the horizontal field strength of a directional antenna should be reduced (in dB) to achieve the smallest efficient downtilt angle?12th February 2008 at 10:03 #50829PixGuest
That could be fun… but I can’t even understand the question 🙂
How many dB’s of attenuation shall be set in order to achieve the smallest tilt ? Yeah… i really don’t understand. Can you clarify ?12th February 2008 at 10:26 #50830Huawei RFGuest
I’m glad that you have found it funny…
I will reform the question:
When we make a downtilt to a directional antenna, we are actually decreasing the field strength of it’s main lobe.
How many dBs we need to decrease that field to achieve the minimum down-tilt?
for example, we want to scale an antenna down-tilt from 1 to 15. 1 is the minimum degree. How many dBs we need to decrease the field strength to scale it as one degree?
firstname.lastname@example.org February 2008 at 12:26 #50831PixGuest
i’m sorry to be such party-pooper (i still think the contest idea is fun though), but you can’t just “reduce the field strength” of an antenna.
What you can do is change the antenna pattern, thanks to mechanical or electrical tilt, or reduce the BTS power…
If your question is : with one degree downtilt, how much rxlev do you loose at cell border ?
Then there is still no answer : it depends where your located compared to the antenna, and what is the antenna pattern (especially the vertical HPBW).
i’m a party pooper, OK…12th February 2008 at 15:08 #50832m@uGuest
I still do not catch the question. LOL
But, when we do downtilt we do not decrease que field strength, we tilt the pattern, the gain is almost the same but in a different angle, which in a horizontal plane will show you as a reduction in the gain.12th February 2008 at 15:31 #50833pixGuest
m@u, thanks, i was afraid to be the only one… 🙂 So i’m not that senile yet !12th February 2008 at 16:07 #50834Huawei RFGuest
Sorry for dissapointing you fellows, but my idea is the correct one!!
What is an antenna pattern? it is the shape of the field strength radiated by the antenna!!
So, Mr. m@u, when we tilt the pattern, the strength will be reduced in the horizon and the radiated power in the cell
that is actually to be covered, increased.
that is because the vertical pattern of an antenna radiates the main energy towards the horizon and only that part of the energy which is radiated below the horizon can be used for the coverage of the sector.
Here, I will answer the question:
Considerable limitation is achieved if the radiated power in the horizon is limited by 6 dB. This means that one can easily predict the smallest efficient tilt angle by simply tilting the vertical radation pattern until the field strength in the horizon is reduced by 6 dB.12th February 2008 at 16:12 #50835Huawei RFGuest
If you guys agree with me, I can put my next question.12th February 2008 at 17:00 #50836paraHOGuest
So is the answer 6db per 1-degree as I is the minimum degree?12th February 2008 at 17:28 #50837Huawei RFGuest
The answer is that the minimum effectice downtilt is when the signal strength decreased by 6 dB.
However, it doesn’t mean that 1 degree mechanical or electrical downtilt will decrease that amount.. it depends on the designer of that tilt scale..13th February 2008 at 05:00 #50838NarChaiGuest
became to reading13th February 2008 at 08:24 #50839PixGuest
I’m sorry, but whatever way you put it, your idea is “reversed”. How can you measure the rxlev at the horizon ? And why 6dB ?
1. For each antenna pattern, in order to achieve 6dB attenuation at horizon, a certain tilt is required. Not all antennas need the same tilt to achieve this…
2. The most effective tilt is found by computing the distances (geometrically) between :
the BTS location and the 0dB point
the BTS location and the -3dB point (upper)
3. When you cover large areas, you certainly want your horizon to be covered as much as possible.13th February 2008 at 11:35 #50840Huawei RFGuest
Well, I did my best to make it clear.. but it seems that I wasn’t lucky…
Anyway, I have uploaded a document discusses the same Idea, may be you can believe me after checking it:
I will put another question though:
What do we mean when saying “the system possesses perfect power control”?13th February 2008 at 19:33 #50841AbdelGuest
The link is dead.14th February 2008 at 04:58 #50842Huawei RFGuest
no its ok!