What are beamformers good for? And why do they need to be reconfigurable when used on a satellite?
Once in orbit, the key task of every satellite is based on the transmission and reception of electromagnetic waves. These waves carry all the information that is necessary to provide for example a certain channel on your TV or to explore the Earth’s surface. Due to the spherical shape of our planet it is obvious that at a particular time, only certain parts of the Earth can be in contact with a satellite while other parts are out of reach. But that’s all right because many services are only needed in a certain area. In fact, it is often essential that a satellite reaches only users that are located within a specific region, for example to provide a TV channel that is only available in your country. But which part of the satellite takes care that information arrives only at relevant points on Earth?
Correct – it’s the beamformer! The beamformer is only one part of the satellite’s antenna system but as you’ll see, it packs quite a punch. We should have a look first on what would happen if a satellite was launched without beamformer. As shown on the left below (not to scale), the antenna of a satellite emits electromagnetic waves which spread as distance increases.
Since a satellite is very far away in space, only a smaller (and in this case random) portion of the transmitted waves will impinge somewhere on the Earth’s surface, while a major part will be lost. To avoid this, the satellite is equipped with a beamformer (below depicted as a crescent).
As shown in the figure, this allows us to direct or form the emission of waves so that as many as possible of them reach the Earth’s surface. But this is rather the very basic task of every satellite antenna. The beamformer itself makes sure that the transmitted information strikes the region on Earth where it is actually needed, that is within a certain footprint, such as a single country or a whole continent. In many cases it is also useful to have a beamformer that allows the satellite to communicate with two or more separate regions at the same time.
So far, so good – but there is an important point that we must not forget: everything goes round. More precisely, the Earth rotates around its axis and the satellite orbits around the Earth. This is no big deal for geosynchronous satellites which appear to be at a fixed point in the sky if you could spot them from ground. But to follow the Earth’s rotation, they need to be placed at a very large distance. This is not always unproblematic because the further a satellite is away from us, the longer it takes to transmit and receive information. A satellite at lower altitude, by contrast, is able to communicate much quicker with us but he does not remain at a fixed position relative to Earth. Here it gets tricky if we want to make sure that we don’t loose connection once the satellite has passed us. In fact, a stable connection is only possible if more than one satellite is used so that every time a satellite leaves our field of view, a following one on the same orbit takes over. It seems like things are getting costly at this point. Is the beamformer of any help here?
The answer is…yes, if it is reconfigurable! To make it more clear, “reconfigurable” means that the way the beamformer shapes and directs the emission of waves can be adjusted. This flexibility opens up a lot of possibilities and allows us to do fancy things with a beamformer. In the previously mentioned case with multiple satellites we can use the beamformer for example to track a target zone on Earth. In this way, a satellite can stay in connection with a certain point for a longer time during each orbital period. This has the great advantage that we get by with a lower number of satellites in space. But take a look at this video – it should give a bit more of insight into what is actually going here.
The reconfigurable beamformer helps us here every time the satellite orbits our planet, that means it works in a recurring manner and for the long term. But there are also sporadic scenarios where this flexibility is of great help. Imagine for example the Olympic games are just around the corner. In this case, reams of information need to be transmitted from and received within a relatively small area on Earth, but all that only for a couple of weeks. Satellites that are equipped with such beamformer can then be used to focus all capacity, for a certain amount of time, on the region where the event takes place. That’s all very well, but what is it that I am actually working on?
Well, obviously we are able to control a beamformer remotely from ground every time we want to reconfigure it. But resources are limited on a satellite and we can’t afford moving the whole bulky antenna system whenever we wish to sweep the satellite’s footprint on Earth. Instead, it would be much better if only a tiny part within the beamformer was adjustable – and this is what I am looking for. In fact, it might be even possible to do that without any mechanical movement at all, but more on that very soon.