Gsm tower

[PG1995]

Hi

I have always been interested in knowing the reason behind the different variety of antennas on a GSM tower. You can see here that antennas vary in sizes and shapes. Could you please briefly tell me that why there are so many different antennas? Or, please point me to a link with information on this topic. I wasn't able to find any good link. Thank you.

Regards
PG

 

[JimB]

At the very top of the tower, we have what I assume to be a lightning conductor. Best place for it to catch the big ziggies from the sky!

The flat panel antennas are the cellphone system antennas.
I am not sure of their physical construction, but note that they are pointing in a slight downward direction.
Because the cell has a limited area, the antenna is tilted to direct the main lobe of the radiation pattern into the intended service area rather than to the horizon which would give maximum range.

The parabolic antennas are used for point to point links to similar communication towers etc.
The diameter of the dish is determined by the frequency in use and the required gain of the antenna.
Some of these links may be part of the cellphone network, others may be part of some other system.

JimB

 

[PG1995]

Thank you, JimB.

The parabolic antennas are used for point to point links to similar communication towers etc.

The point-to-point links would mean that the towers can see each other without any obstacle between them such as a tall building, right? It would also mean that the number of parabolic antennas tells how many towers the tower is communicating with.

The diameter of the dish is determined by the frequency in use and the required gain of the antenna.

What does a smaller size parabolic antenna tell us about the frequency in use and the gain? Is it using lower or higher frequency?

Thanks.

Regards
PG

 

[JimB]

The point-to-point links would mean that the towers can see each other without any obstacle between them such as a tall building, right?

Yes.

It would also mean that the number of parabolic antennas tells how many towers the tower is communicating with.

Generally, Yes.
But, it could be that there are two antennas at different heights carrying exactly the same link.
This could be for redundancy, so that if one antenna or its feed line failed, there would be a back-up antenna,
or, more likely for diversity.
If the characteristics of the radio path are likely to change, such as a link which crosses a tidal stretch of water where the received signal strength can vary considerably due to changing path lengths for the signal reflected from the water surface, the antennas are separated by a suitable distance so that the both do not see a signal strength minimum at the same time.

What does a smaller size parabolic antenna tell us about the frequency in use and the gain?

For a given antenna gain, the longer the wavelength, the bigger the antenna.
The longer the wavelength - the lower the frequency.
So, bigger antenna - lower frequency. Smaller antenna - higher frequency.

JimB