INTRODUCTION
With Starlink internet, data is continuously being sent between a ground-based dish and a Starlink satellite orbiting 550km above. Furthermore, the Starlink satellite zooms across the sky at 27,000km/hr! How can the dish and satellite maintain a continuous connection? And then how is data sent back and forth? Well, in this article we're going to explore into the inner workings for the ground dish and Starlink satellites, and see how a beam of data is formed, how this beam is swept across the sky, and then finally what exactly is inside that beam that allows for incredibly fast internet! This is an incredible feat of technology and engineering, so stick around and enjoy the reading!
Beaming internet from the middle of a building, using an extra-large pizza-sized satellite dish placed on top of your building, up to a satellite orbiting 550 kilometers outside Earth’s atmosphere, well let’s be honest, is technologically mind-blowing. What’s even crazier is that the Starlink satellites move incredibly fast, around 27,000 kilometers per hour, and data is being sent back and forth between them at hundreds of megabits per second, all while the dish and satellite are continuously angling or steering the beam of data, pointed directly between them. On top of that, the dish switches between different satellites every 4 or so minutes, because they move out of the dishes’ field of view rather quickly. If you have no clue as to how this is possible and you’re curious to know how all these are possible, stick around, because we’re going to dive into the multiple key technologies which enable satellite internet to magically work.
Overview of Starlink Stallites and Dishes
First, we’ll explore inside the satellite dish and see how it generates a beam of data that is able to reach space. Second, which will be in the next post, we’ll see how this dish continuously steers the beam so that it points directly at a satellite moving across the sky. And finally in another post, we’ll dive into what exactly the dish and satellite are sending inside the beam that results in our ability to stream 5 HD movies or shows simultaneously. But before we dive into the details on what constitutes the Starlink satellite and its dish, and how they work, let’s explore the little differences between the satellites used for TV broadcasting and the one used in Starlink satellites.
So, stick around, and let’s jump right in!
Difference between Starlink and Broadcast Satellites
Let’s start by clarifying the difference between a television satellite dish such as the one below, and the Starlink ground dish, which Elon Musk dubbed Dishy McFlatface or Dishy for short. TV dishes use a parabolic reflector to focus the electromagnetic waves which are the TV signals sent from broadcast satellites orbiting the Earth at an altitude of 35,000 kilometers. TV satellite dishes only receive TV signals from space, they can’t send data.
Parabolic TV Satellite Dish
Dishy, however, both sends and receives internet data from a Starlink satellite orbiting 550 kilometers away. While the Starlink satellite is 60 times closer than TV satellites, it’s still an incredible distance to wirelessly send a signal, and thus the beams between Dishy and the Starlink satellite need to be focused into tight powerful beams that are continuously angled or steered to point at one another.
Starlink Dishy McFlatface (First generation – Gen_1 rounded dish, and the second generation – Gen_2 dish)
Compare this beam signals of Starlink satellites to TV broadcast signals which come from a satellite the size of a van, and whose signals propagate in a wide fan that covers land masses larger than 24.71 million km². Table size Starlink satellites, however, need to be in a low earth orbit to provide for 20-millisecond latencies – the round trip data time between the user and satellite, which is critical for smoothly playing internet games or surfing the web, and as a result, their coverage is much smaller. Thus 10,000 or more Starlink satellites, all orbiting at incredibly fast speeds in a low earth orbit, are required to provide satellite internet to the entire earth.
Starlink satellites first batch of second-generation gen 2, which the SpaceX company calls “V2 Mini.
Credit: SpaceX
INSIDE THE DISHY (Starlink Ground Dish)
It is time for us now to open up Dishy McFlatface. At the back, we have a pair of motors and an ethernet cable that connects to the router. Note that these motors don’t continuously move Dishy to point directly at the Starlink satellite, they’re used only for initial setup to get the dish pointed in the proper general direction.
Back openings of the dishy showing the pair of motors used in initial setup.
Opening up Dishy, we find an aluminium structural back-plate and on the other side, we find a massive, printed circuit board or PCB. One side of the PCB has 640 small microchips and 20 larger microchips organized in a pattern with very intricate traces fanning out from the larger to smaller microchips, along with additional chips including the main CPU and GPS module on the edge of the PCB. On the other side are 1,400ish copper circles with a grid of squares between the circles.
On the next layer, there’s a rubber honeycomb pattern with small, notched copper circles, and behind that, we find another honeycomb pattern and then the front side of Dishy. Well, in essence, there are 1280 antennas arranged in a hexagonal honeycomb pattern called Aperture Couple Patch Antenna, with each stack of copper circles being a single antenna controlled by the microchips on the PCB. This massive array works together in what’s called a phased array in order to send and receive electromagnetic waves that are angled to and from a Starlink satellite orbiting 550 kilometers above.
Layers of components inside the Starlink dishy.
How Does an Aperture Couple Patch Antenna Work?
The aperture coupled patch antenna of the Starlink dishy is composed of 6 layers, printed on the PCB inside the dishy. It looks very different from the antenna of an old-school radio. So, let’s explore it. To start, at the bottom of the antenna, there is a microstrip transmission line feed coming from one of the small microchips. This transmission line feed is just a copper PCB trace or wire that abruptly ends under the antenna stack.
Stack of copper circles being a single antenna on the Dishy PCB.
A 12 Gigahertz high-frequency voltage or signal is sent to the feed wire which is a voltage that goes up and down in a sinusoidal fashion, going from positive to negative and back to positive once every 83 pico-seconds, 12 billion times in a second, or 12 Gigahertz. Note that high-frequency electricity works differently from direct current or low frequency 50 or 60-hertz household electricity.
For example, above the copper feed wire, there is a copper circle with notches cut into it called an antenna patch. With DC or low-frequency alternating current, there wouldn’t be much happening because the patch is isolated, but with a high-frequency signal, the power sent to the feed wire is coupled or sent to the patch. How exactly does this happen?
Well, as mentioned earlier, a 12 Gigahertz signal is applied to the copper feed wire. When the voltage is at the bottom of its sinusoidal, or trough, there will be a concentration of an electrons pushed to the end of the feed wire, thus creating a zone of negative charge which corresponds to the maximum negative voltage.
This concentration of electrons on the tip of the wire repels all electrons away, including the electrons on the top of the patch, and as a result, these electrons are pushed to the other side of the circular patch. Thus, one side of the patch becomes positively charged, while the other becomes negatively charged, thereby creating electric fields between the patch and feed wire like so.
However, when the voltage was reversed to the copper feed wire 42 picoseconds later, there would be a concentration of positive charges, or a lack of electrons at the end of the wire, and thus the electrons in the patch flow to the other side, the voltage in the patch is flipped, and the direction of the electric fields are also flipped. Because the feed wire voltage oscillates back and forth, 42 picoseconds between one peak and trough, the electric fields in the patch will also oscillate as the electrons, or current, flows back and forth. If the oscillation is to be pause, some of these electric field vectors, or arrows, from the patch, are going to be in vertical direction, and because they are equal and opposite, they cancel out.
However, other electric fields are horizontal in the same plane of the patch and are called fringing fields. These fringing fields are in the same direction and thus they add to each other, resulting in a combined electric field pointing in this direction. At the same time, electrons flowing from one side of the disk to the other, which is an electric current, generate a magnetic field with a strength and direction, or vector, perpendicular to the fringing electric field vector. As a result, we have an electric field pointing one way, and a magnetic field pointing perpendicular to that.
Electromagnetic Wave Emission
Let’s move forward in time to where the voltage on the feedline becomes positive, and now, we’re at the peak of the sinusoid, 42 picoseconds later. The charge concentrations, or voltage, as well as the current, is all flipped, and thus the electric and magnetic fields point in the opposite directions. Electric and magnetic fields propagate in all directions, and by creating these oscillating fields, an electromagnetic wave generated which travels in the direction perpendicular to both the electric and magnetic field vectors. Because the two sets of field vectors are not all in the same plane, but rather are curved, the propagating electromagnetic wave travels outwards in an expanding shell or balloon-like fashion, kind of like a light bulb on the ceiling.
If for instance we’re to only see the peak and trough or top and bottom of each wave and note that the trough is just a vector pointed in the opposite direction. Additionally, the strengths of these field vectors directly relate back to the voltage and signal that was originally sent to the copper microstrip feed wire at the bottom of the stack. Which means, if these electric and magnetic fields are to be make stronger, the voltage sent to the feedline has to be increase. It’s like a dimmer on a light switch: more power equals a brighter light.
Thus far we’ve been talking about this aperture-coupled patch-antenna as transmitter. However, it can also be used for receiving a signal. In one microchip, called a front-end module, the antenna is switch from transmitting to receiving and turn off the 12 Gigahertz signal. When an electromagnetic wave from the satellite is directed towards Dishy, the electric fields from this incoming signal will influence the electrons in the copper patch, thus generating an oscillating flow of electrons. This received high-frequency signal is then coupled to the feedline where it’s sent to the front-end module chip which amplifies the signal. Thus, these antennas can be used to both transmit and receive electromagnetic waves, but, not at the same time.
Two quick things to note: First, as described earlier, this antenna has many more layers and is more complicated than we’ve discussed. For example, the diagram below are two circular patches. The bottom is used to transmit at 13 Gigahertz while the top to receive at 11.7 Gigahertz. Additionally, there are two H slots and two feed wires to support circular polarization, a reflective plane in the back, and also, there are multiple features for isolating the operation of one antenna from the adjacent antennas.
Two circular patches layer of the Antenna.
The second note is that there are electromagnetic waves of all different frequencies from thousands of different sources passing through every point on Earth, whether it be visible light from the sun, radio waves from radio or cell towers, or TV signals from satellites or towers. Therefore, in order to block out all other frequencies of electromagnetic waves, these antenna patches are designed with very exact dimensions so that they receive and transmit only a very narrow range of frequencies, and all the other frequencies outside this range are essentially ignored by the antenna. Let’s move on and see how a single antenna can be combined with others in order to amplify the beam to reach outer space.
Forming a Beam that Reaches Space: Beamforming
A single aperture coupled patch antenna of the Starlink dishy is only a centimeter or so in diameter and using only it would be like turning on and off one light bulb and trying to see it from the international space station. What needed now is a way to make the light a few thousand times brighter, and then focus all the electromagnetic waves into a single powerful beam. Entering the massive Mr. McFlatface PCB, 55 centimeters wide with a total of 1280 identical antennas in a hexagonal array. The technique of combining all the antennas’ power together is called beamforming. So how does it work?
Well, let’s first observed what happens when there are two simplified antennas spaced a short distance away. As mentioned earlier, one antenna generates an electromagnetic wave that propagates outwards in a balloon shape.
At every single point in space, there’s only one electric field vector with a strength and direction and thus the two antennas’ oscillating electric field vectors combine together at all points in space. In some areas, the electric fields from the antennas are pointing in the same direction with overlapping peaks, and thus add together via constructive interference, and in other locations, they’re opposite with one peak and one trough, and thus they cancel each other via destructive interference.
We can now understand that the zone where they add together constructively is far tighter, or more focused, than a single antenna alone. When more antennas are to be added, the zone of constructive interference would become even more focused in what is called a beam front. Thus, by adding 1280 antennas together, a beam with so much intensity and directionality can be form that can reach outer space. Now you might be thinking that the strength of 1 antenna duplicated 1280 times over would result in a combined power of, well, 1280 times a single antenna, but you’d be mistaken. The effective power and range of the main beam from all these antennas combined is actually closer to 3500 times that of a single antenna. The quick explanation is that by having these patterns of constructive and destructive interference, it’s as if we took a single antenna, multiplied it by 1280, and then placed a whole bunch of mirrors around it and left only a single hole for the main beam to exit through.
To continue reading on how the Starlink dishes and satellites works, clicks on the next topic below:
Starlink Dish and Satellite! How it Works? BEAM STEERING
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