3 ms·

I've been playing with antenna phasing and I have a preliminary result for three cellular antennas: http://i.imgur.com/tyyVh0j.png http://i.imgur.com/tyyVh0j.p

by lutusp 13y ago

I've been playing with antenna phasing and I have a preliminary result for three cellular antennas: http://i.imgur.com/tyyVh0j.png http://i.imgur.com/tyyVh0j.png The antenna locations are marked with blue dots. In this diagram the size of the high-signal-strength lobes is much larger than would be true at cellular frequencies, but it gives a sense of how this idea works. By adjusting the phase at each antenna, the lobes can be moved around to accommodate different devices within their range. As I expected, increasing the number of antennas past three doesn't really improve the outcome enough to justify the increased complexity.

TTPrograms 13y ago
This is called phased array, and it's been around since WWII for radar applications: https://en.wikipedia.org/wiki/Phased_array https://en.wikipedia.org/wiki/Phased_array More antennas can enable you to narrow lobes more - you may have not been phasing them properly to get that effect.
- darkmighty 13y ago
  Yea, and MIMO is should be not only beamforming (which, best case scenario, gives you one strong channel); but it uses multipath to create essentially two channels at the same frequency.
- lutusp 13y ago
  My sole reason for posting the example was to show how a small number of individual antennas could produce focusing lobes within a 2D space. Phased array radars use many more elements, much higher control over the wavefront, and for a different purpose. In a cellular antenna scenario, unlike phased array radar, you cannot avoid multiple lobes, but the advantage of phasing is still present. Adding antennas to the system (beyond three or four) becomes a case of diminishing returns. > More antennas can enable you to narrow lobes more - you may have not been phasing them properly to get that effect. There are paradoxical effects with more than a few antennas -- apart from the complexity issue. In some cases you will see lobes with strange shapes in locations having no benefit. With a circular array of antennas, you sometimes get concentric circles of high signal strength, not what you're after in the described system. Example: http://i.imgur.com/hK9BZnF.png http://i.imgur.com/hK9BZnF.png
  - TTPrograms 13y ago
    I'd recommend you make your system scale appropriate. Considering that cellular transmissions are on the order of GHz, you're effectively simulating a circle of antennas around 1 m wide looking at what happens in the middle. That doesn't seem particularly relevant to the case of antennas being very far away (far-field vs near-field etc).
    - lutusp 13y ago
      Yes, understood. The diagram was only meant to show how interference works, not at all to represent the problem under discussion.
vxNsr 13y ago
Would you mind going into a little more detail about what each color represents. Intuitively, the diagram seems to say that behind (in front of?) each blue dot (antenna) the signal is really strong while on the other side it kinda drops down, only to strengthen again when we hit the middle of the triangle. But I really have no idea what's going on... Thanks.
- lutusp 13y ago
  > Would you mind going into a little more detail about what each color represents. It's a simple density plot of an electromagnetic field in which the brighter colors represent constructive interference and dark areas represent destructive interference. The three antennas constructively or destructively interfere, with varying effects at different locations within the field. I want to say again that the diagram is only an example and uses a frequency much lower than that used by cellular systems, just so the lobes are a reasonable size, and only to give some idea of the principles at work. > Intuitively, the diagram seems to say that behind (in front of?) each blue dot (antenna) the signal is really strong while on the other side it kinda drops down, only to strengthen again when we hit the middle of the triangle. Yes, that's true -- the three external lobes happen to be places where the three antennas constructively interfere. One can do this using pencil and paper (as I did when I was a NASA Space Shuttle engineer many years ago, and before there were personal computers), but computers make it much easier to experiment with different configurations. Here's a different antenna configuration, one that I doubt anyone would want to build -- a circle of antennas, giving circular intensity lobes: http://i.imgur.com/hK9BZnF.png http://i.imgur.com/hK9BZnF.png Not very useful, but interesting.
mdonahoe 13y ago
what did you use to create this plot?

by lutusp 13y ago

TTPrograms 13y ago

This is called phased array, and it's been around since WWII for radar applications: https://en.wikipedia.org/wiki/Phased_array https://en.wikipedia.org/wiki/Phased_array More antennas can enable you to narrow lobes more - you may have not been phasing them properly to get that effect.

darkmighty 13y ago
Yea, and MIMO is should be not only beamforming (which, best case scenario, gives you one strong channel); but it uses multipath to create essentially two channels at the same frequency.
lutusp 13y ago
My sole reason for posting the example was to show how a small number of individual antennas could produce focusing lobes within a 2D space. Phased array radars use many more elements, much higher control over the wavefront, and for a different purpose. In a cellular antenna scenario, unlike phased array radar, you cannot avoid multiple lobes, but the advantage of phasing is still present. Adding antennas to the system (beyond three or four) becomes a case of diminishing returns. > More antennas can enable you to narrow lobes more - you may have not been phasing them properly to get that effect. There are paradoxical effects with more than a few antennas -- apart from the complexity issue. In some cases you will see lobes with strange shapes in locations having no benefit. With a circular array of antennas, you sometimes get concentric circles of high signal strength, not what you're after in the described system. Example: http://i.imgur.com/hK9BZnF.png http://i.imgur.com/hK9BZnF.png
- TTPrograms 13y ago
  I'd recommend you make your system scale appropriate. Considering that cellular transmissions are on the order of GHz, you're effectively simulating a circle of antennas around 1 m wide looking at what happens in the middle. That doesn't seem particularly relevant to the case of antennas being very far away (far-field vs near-field etc).
  - lutusp 13y ago
    Yes, understood. The diagram was only meant to show how interference works, not at all to represent the problem under discussion.

vxNsr 13y ago

Would you mind going into a little more detail about what each color represents. Intuitively, the diagram seems to say that behind (in front of?) each blue dot (antenna) the signal is really strong while on the other side it kinda drops down, only to strengthen again when we hit the middle of the triangle. But I really have no idea what's going on... Thanks.

lutusp 13y ago
> Would you mind going into a little more detail about what each color represents. It's a simple density plot of an electromagnetic field in which the brighter colors represent constructive interference and dark areas represent destructive interference. The three antennas constructively or destructively interfere, with varying effects at different locations within the field. I want to say again that the diagram is only an example and uses a frequency much lower than that used by cellular systems, just so the lobes are a reasonable size, and only to give some idea of the principles at work. > Intuitively, the diagram seems to say that behind (in front of?) each blue dot (antenna) the signal is really strong while on the other side it kinda drops down, only to strengthen again when we hit the middle of the triangle. Yes, that's true -- the three external lobes happen to be places where the three antennas constructively interfere. One can do this using pencil and paper (as I did when I was a NASA Space Shuttle engineer many years ago, and before there were personal computers), but computers make it much easier to experiment with different configurations. Here's a different antenna configuration, one that I doubt anyone would want to build -- a circle of antennas, giving circular intensity lobes: http://i.imgur.com/hK9BZnF.png http://i.imgur.com/hK9BZnF.png Not very useful, but interesting.

mdonahoe 13y ago

what did you use to create this plot?