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Phased array antennas do not put all of the power into a spot and then no power elsewhere. It's all about the ratios and the distribution. This example is from

Phased array antennas do not put all of the power into a spot and then no power elsewhere. It's all about the ratios and the distribution. This example is from the wikipedia article on directional antennas: https://en.wikipedia.org/wiki/Directional_antenna#/media/File:Patch_antenna_pattern.gif https://en.wikipedia.org/wiki/Directional_antenna#/media/Fil... This is the standard way of showing the performance of antennas - it shows the varying amount of power that is sent out from the antenna in different directions. Note that (a) it doesn't roll off immediately outside the target zone (usually the 3dB threshold as shown here) and (b) there is measurable power in completely off-axis directions. In fact the tighter you beam steer, the more lobes you get in weird places. Both of these mean that you can't just parcel up physical space into perfect beam spots and just keep adding satellites. There are all sorts of things you can do to help as you go up, but it gets harder and harder.

Retric 4y ago
That's true, but assuming maximum possible density both the sender and receiver should be using directional antenna on top of this the closest satellite gets the strongest signal simply due to distance. That distance effect becomes less meaningful as the density increases but stays relevant for practical networks.
- rkangel 4y ago
  Both ends of the starling link are already using directional antennas. The difference in power die to distance is already pretty irrelevant - the satellite is 400km up and we're talking about offsets of 10km on the ground. The 400km part of that is far more dominant making the power difference to the 'next satellite over' be very small.
  - Retric 4y ago
    “Both ends of the starlink are already using directional antennas” Sure, but it’s critical to understand the associated benefits when doing this kind of analysis. If you’re talking average 10km separation on the ground that would mean stupid high constilation densities. A lower densities it’s more meaningful. PS: I got to 1 billion customers assuming different hardware and more satellites not just more satellites. The only way 100,000 customers “works” is a none viable and lower bandwidth per customer business model, but the goal was to illustrate a point. Space X is aiming for an economic sweet spot, not the outer edge of what’s technically possible.

Retric 4y ago

That's true, but assuming maximum possible density both the sender and receiver should be using directional antenna on top of this the closest satellite gets the strongest signal simply due to distance. That distance effect becomes less meaningful as the density increases but stays relevant for practical networks.

rkangel 4y ago
Both ends of the starling link are already using directional antennas. The difference in power die to distance is already pretty irrelevant - the satellite is 400km up and we're talking about offsets of 10km on the ground. The 400km part of that is far more dominant making the power difference to the 'next satellite over' be very small.
- Retric 4y ago
  “Both ends of the starlink are already using directional antennas” Sure, but it’s critical to understand the associated benefits when doing this kind of analysis. If you’re talking average 10km separation on the ground that would mean stupid high constilation densities. A lower densities it’s more meaningful. PS: I got to 1 billion customers assuming different hardware and more satellites not just more satellites. The only way 100,000 customers “works” is a none viable and lower bandwidth per customer business model, but the goal was to illustrate a point. Space X is aiming for an economic sweet spot, not the outer edge of what’s technically possible.