Feed Antennas

Being already in 2018 there is no doubt that satellite communications are an integral part of our life. Although not visible from earth, their importance can be met in a wide range of services. Just imagine the two most common facts: Using a positioning system to track yourself in an isolated place and using your smartphone to communicate with other people or have access to multimedia. Obviously, the satellites can provide these kind of services in an excellent way, whereas there is a great variety of further applications where their use is vital as well, such as weather prediction and space exploration to name a few.

Satellites are in principle big and complex structures, where many components are assembled together so that the satellite can be launched from the earth to the space. One of the most significant part of a satellite is the antennas. If we could compare a satellite with a human, the antennas are “the eyes and the ears”. You can easily understand that without the antennas, a satellite cannot communicate with nobody and after all has not a reason to exist!

Here at REVOLVE we are doing research around antennas for satellites as you may already know. Every one of us studies different aspects and technologies. In a very fundamental analysis, the antennas implemented and used on satellites can be categorized into two principal domains: the so called Focal Array Fed Reflectors and the Direct Radiating Antenna Arrays. In the first category belong the typical parabolic structures fed by the so called feed-antennas (usually horn antennas) which are more or less widely known, whereas in the second single antennas are formed in an array and they radiate themselves.

My subject of research concerns the feed antennas. These antennas are almost always the typical horn antennas, which are used many years now because of their great performance. Although they are described as feed antennas this might be a bit confusing or misleading as the same antennas could be used as direct radiating arrays without the presence of a reflector. In any case, my 3 year journey at REVOLVE will go through the different existing technologies around the feed antennas and we will try to find out how we could make them function better and in a more compact shape as the current solutions have a bulky profile.

At last, somebody might wonder…so what is it so important about it? There may be many things important that neither myself could even recognize, but as I mentioned earlier the satellites are big and complex structures so imagine how important would be if we could provide something smaller and lighter. Furthermore, think about that this “something” are the antennas which constitute a very basic and important part of a satellite and after all we are moving ahead to the 5G era and the next years a great increase in the multimedia usage and communication services is about to take place, so we need to confine with these rules.

Lens Antennas

Lens antennas are a very attractive solution in space applications because they can provide high directivity beams. A specific type of Lense is called a ‘graded index lense’. This type of antenna is composed of periodic structures that have variable refractive indexes and can convert spherical waves into plane waves. Thus, we can focus the beam and steer it. As the aim is to integrate this antenna into the satellite we also need to make it more compact as well as provide multiple beams to cover multiple countries. In addition to the multiple beams that we need to provide we also need to achieve isoflux radiation pattern in the multibeam antenna. Practically, this type of pattern means that if we want to cover a country that is in the direct path of the satellite we need less gain than a country which is placed some angles from the satellite. Ideally, a 3D graded index Lens would be the best candidate for LEO and GEO satellites because we will be able to steer the beam in both E and H planes and thus cover multiple countries.

Well, I believe that some of these technical expressions might be tough to understand but when you begin to understand the meaning you can begin to be more interested in the space domain and the antennas. Talking to young students that are in high schools and in the universities, I would like to encourage them to become involved in space engineering and electromagnetics and my job will be to simplify the meanings. After that you will really the subject and be more passionate with it.

Advanced Synthesis of Reflect-Arrays

It is very likely to be that if you think about a space antenna, the image that appears in your mind is a parabola that sends electromagnetic waves toward the Earth or the deep space. An antenna, as it appears, is a metallic structure that captures and/or transmits radio electromagnetic waves. Antennas come in all shapes and sizes from little ones that can be found on your roof to watch TV to really big ones that capture signals from satellites millions of miles away (figure 1). The antennas that space satellites uses are a special bowl shaped antenna that focuses signals at a single point called a parabolic antenna. The bowl shape is what allows the antennas to both capture and transmit electromagnetic waves.

via GIPHY Figure 1 New Horizon mission spacecraft, a courtesy of jpl.nasa.gov

But what if this concept of capturing and/or transmitting electromagnetic waves would be performed in a slightly different way? Keeping in mind that a parabolic or shaped antennas exploits the geometric features of the reflecting surface to create a narrow and symmetric antenna beam, we can imagine to exploit another concept to perform this signal directivity.

The concept of a Reflect-Array is based on the fact that we want create this narrow and symmetric beam by using flat reflector, or we can say, flat antennas. This is the key point of the Reflect-Array technology. So, does not matter which kind of signal or for which application, a spacecraft would be equipped by a flat antenna.   The simple geometric shape of this kind of antenna would allow to reduce the cost of manifacturing, would allow a more flexible allocation on the spacecraft, since it can be conceived foldable, it can be lighter (reduction of mass in Space satellite is very important) and, last but not the least, it can offer a very performing and smart technology for space application.


Figure 2: C-band Reflect-Array demonstrator, a courtesy of Thales Alenia Space France

Another milestone concept of Reflect-Array is that it is constituted by a flat panel that is printed with several metallic patches. Electromagnetic waves can be reflected in different way if they imping of different surfaces, in this case on different patches. The way the signal is reflected by every single patch will determine an ensemble of small signals that interact, they sum up or erase each other. The result is a directive narrow signal as would be produced by a traditional shaped antenna.

Figure 3: Deployment scheme of a faceted Reflect-Array, courtesy of Thales Alenia Space France.

Mechanically Reconfigurable Antennas

In October 2017 I began my PhD and every time I answer the question, “What do you do?”, the next question would be, “What is your subject?”

The first time I answered whilst quoting the e-mail describing the job, “My PhD is part of the REVOLVE project which is a European initiative dealing with the study of the Smart Reflector Surfaces with processing capability based on actuated flexible thin organic large area surfaces.”

The second question, ‘What is your subject?’ took me by surprise and led me to create my PhD title: ‘Mechanically Reconfigurable Antennas.’ At this moment I was very proud of myself as I had finally found a way to explain what I will do using a title that people can understand. I looked at the eyes of my interlocutor and I understood that what I had described was not very clear. Describing or explaining something is much more difficult than trying to find a title, even more when you already have read a lot of papers about the subject area and when you try to interest people. It is my purpose on the blog to try and do this so do not hesitate to comment or to ask questions – I am still learning!

The first step to clarify a subject is to know more about the general context.

What is the context of the ESR5 ?

The REVOLVE project is a European initiative aimed at developing new solutions for future satellite systems. It will aim to investigate new technologies that will make the satellites easier to build and cheaper thus gaining time and reducing costs which is very important for industries. Moreover, the growth of the technical improvement is very fast and it is important to adapt in order to be competitive in the market.

The second is to understand a subject, and it is important to know the meaning of each word used :’ Smart Reflector Surfaces with processing capability based on actuated flexible thin organic large area surfaces’.

What is a Smart Reflector Surfaces for antenna?

In this PhD, the ‘Smart Reflector Surfaces’ will be a reflectarray. What is a reflectarray ? It combines some features of reflectors and of array antennas. A reflector antenna is a device that reflects electromagnetic waves while the array antennas is composed of groups of radiating elements which are distributed and oriented in a specific configuration. I have described two interesting experiments around Smart Reflector Surfaces for Antenna below:-

Experiment 1:

Take one curved mirror and a flashlight. Turn off every light. Illuminate the curved mirror with the flashlight, you will see on the wall in front of the mirror a circular lighted zone : it is the same process for the reflector antenna. The light rays are replaced by the electromagnetic waves which are directed on a precise zone on the Earth (see below)…



Experiment 2:

Take four plane mirrors and a flashlight. Turn off every light. Gather all the mirrors together but give them different orientation. Illuminate all the mirrors simultaneously with the same flashlight, you will see on the wall in front of the mirrors a lighted zone : it is the same process for the array antenna. Same as before, the light rays are replaced by the electromagnetic waves which are directed on a precise zone on the Earth. Nevertheless, it is important to note that the impact of the given incidence of the miror is equivalent of the array radiating elements geometry.

In conclusion, the reflectarray combines the simplicity of the reflector antenna with the performances of the array type. In fact, the reflectarray is a planar reflecting surface with a lot of radiating elements.

What is the meaning of processing capabilities?

As it is presented before, the technologies and the market change continuously and it is important to have an overview of all the possible applications a system could manage. For an antenna it could be : radio applications, space tracking or communications.

Furthermore, the main goal of this subject is to be able to reconfigure the antenna. We could say that for one mission, for exemple a satellite place at 500km of altitude which as to cover France, the antenna has one fixed shape and the satellite will be design and product during approximately 10 to 15 years. In conclusion what we ask now will be in-orbit in 2028-2033, it is too long as regard of the needs growth.

The figure below presents one cell phone of the year 2003:




 What is TOLAE (Thin Organic Large Area Surface)?

It is an emerging technology and is the goal is to have a large area electronics that are thin, light weight, flexible and/or stretchable, suitable for large market sectors.

Why do we need TOLAE?

To reconfigure an antenna we could do it electromagnetically or mechanically. In my PhD we will try to do it with the second possibility in order to increase the fiability of the final system. If we take the hypothesis presented before : one shape of the antenna for one mission. So if we change the shape we change the mission and so the targeted zone on Earth, but it is quite more complicate.

To simplify the reflectarray is made of two layers separated by vacuum. On the upper layer you have the radiating elements which are illuminated by a feed (the flashlight). The electromagnetic waves will pass through this layer and be re-radiated by the second layer (the ground plane) in one direction.

Using the principle of the second experience presented before, if we modify the shape of the second layer, we will change the specification of the missions. To do it we could use some actuators which will push on this second layer at different zones and that is why we need a flexible surface.

In conclusion, the main purpose of my PhD is to find a mechanical way to change in-orbit the mission’s specifications which has to be lightweight, cheap and simple.










Linked to a Satellite!

Imagine you are lost in one of the most remote place in Antartica or in the Amazonian jungle, it seems like all hope is gone and your life is about to reach an end… Except if you are properly linked to a satellite!


Figure 1 – Telephone linked to the satellite constellation Iridium manufactured by Thales Alenia Space

Then you can call anywhere on the earth and connect to anyone in a snap. The problem is to figure out how the satellite will know when and where to help you and that’s the moment my project comes into place. Louis described the ears of the satellite with mind-boggling antennas, I consider my work has more to do with the brain of the satellite: it must know in which region on earth it must focus its ears. To use specific words, my work is on satellite payload. But why adding a load on a satellite ? This payload is the brain of the satellite, it points the antenna and gives proper amount of power in the correct direction so you can for example communicate or surf the Internet. The payload shares these services with all the people who pays to use the satellite. This may seem easy but sometimes enabling a lot of people to use the satellite at the same time is a problem to pull one’s hair out. Just remember that time you wanted to send a text or make a call at New Year’s Eve. If the network is crowded you must find some way out, it is the same with satellite network so the focus of satellite’s resources must be on the busiest regions. On the contrary, steering the antenna towards Sahara desert would be quite pointless…

Moreover in the case you want to serve a busy area, interference between users becomes a serious problem you must take into account. If you want to have an idea of what interference is, imagine a meeting where everybody is speaking at the same time, the voice of each other would jam the conversation and it would result in a joyful cacophony. Exactly the same phenomena happens in some cases when either the satellite speaks to users on the ground or users on the ground to the satellite. Mitigating these effects is also part of my work.

To wrap it up, my work is to make satellites’ architectures smarter, more flexible to any situation that may occurs whether you are in Antartica at the brink of death or if you just want to wish a happy new year to your loved ones. The video presenting Thales Alenia Space constellation Iridium with worldwide coverage is below:



Deployable structures for antennas

So yes, what am I doing exactly? “Deployable structures for antennas” – what is it? And why does it have to be “deployable”?

When a telecommunication satellite is launched, it’s main goal is to talk with the Earth, to listen on one side, and to repeat the message on the other side. It works a bit like a phone in a way: it allows two people, two computers or two machines to discuss. But a satellite can be very, very far from the Earth, so how can he listen, or talk, to you? He needs really big ears, and a really big megaphone. Ok, the comparison stops there, because it’s not sound but radio waves that are used, and it doesn’t really have ears nor a mouth. But it does have big, sometimes very big antennas.

How big? you see the smallsatellite antenna dish on the roof antennas on the side or the roof of some building, pointing at the sky? Those are actually used to “listen” to TV satellites that broadcats all kind of channels. And they are probably about 50cm in diameter. Well, it is pretty common for satellite antennas to measure 2 or 3 m in diameter! And some are even much bigger: the largest antenna flying measures close to 20m in diameter – that’s a 6 floors building!

80sqvsgfkmEvftZuFcRJwQqiegCe-ORHEnWsmWyy8lcSo now that we have those big antennas (and I have only mentioned telecommunication, but they can also be used for earth or space observation, radars, etc…), how do we launch them? See, the problem is that you cannot put this 20m antenna in a rocket, it would not fit. The last stage of the rocket, where the satellite is, has a diameter of 4m for the biggest rockets. Because of that, even for a “small” 4m diameter antenna, there is only one solution: you have to fold it, and once up there, open it up. There is something really similar that is used really often here, on earth. It can be very small, fit in your bag, but when it rains it get big enough to keep you dry: that’s right, I’m building a giant umbrella, for a satellite.

Does it look like an umbrella? Hmm, not really, but the idea is there. How do you do it then? Well, that’s the whole point of my thesis! I wouldn’t spoil it all and tell you now, right? But as a trailer I can show you what Large Space Structures GmbH, a partner of the REVOLVE project, has been doing recently.

Banner image and video : courtesy of LSS GmbH.
Ariane 5: ESA-CNES-ARIANESPACE-Photo Optique Video CSG

Future space engineers boldly go…

A press release went out today from Heriot-Watt University as we welcome the next generation of space engineers!


Project Coordinator, Professor George Goussetis  explained: “This is the start of an extremely interesting but ultimately exciting journey for these PhD students…the REVOLVE project provides them with a unique, multi-disciplinary learning experience to ensure they are industry ready”.

Later this month the team will travel to Toulouse in France to attend the projects annual workshop at Thales Alenia Space. There they will be joined by representatives from the other agencies involved in REVOLVE.

Further information on REVOLVE can be found via @revolve_project and www.facebook.com/revolve.hwu.7



Cr_NewstartsA warm welcome to our seven new doctoral candidates who have started their programmes as part of the H2020 project REVOLVE. They will spend the next two months at Thales Alenia Space and will be mentored by Hervé Legay from the Research & Technology Department. We very much look forward to hearing more about their time at Thales and in particular, how they meet the challenges inherent in the world of space communications! Updates will follow with regular contributions to this blog by our young researchers…please check back again soon!

Women in Engineering

A new video has been uploaded on the Women in Engineering page!

Dr Rebecca Marr talks about her experience as a civil engineer and researcher within the Institute for Infrastructure and Environment, Heriot-Watt University, Edinburgh.

The Institute for Infrastructure and Environment undertakes cutting-edge research to deliver technological advances and inform government policy on topics relevant to the global challenges of: climate change; sustainable development; infrastructure deterioration; and personal and national security.

Their research includes the specialist themes of water management; ultra-speed railways; systems, sustainability and society; construction materials and geo-mechanics; and structures. Within these themes our staff possess the expertise and experience necessary to undertake projects ranging from ‘blue skies’ research, through research investigations of innovative technologies, to industry sponsored consultancy projects.

Rebecca’s video can be viewed here.


Welcome to REVOLVE Outreach

Juline Legay is presently preparing for her exams for a Business School in France and has created and developed this Outreach Initiative for REVOLVE!

Juline has a strong interest in communication and enjoyed a short internship in the communication department of Thales Alenia Space in Toulouse 4 years ago. This summer, Juline volunteered for a one month internship in Heriot-Watt University, where she worked on outreach activities as part of the Revolve project. She was supervised by Prof. George Goussetis and Dr. Carolina Mateo-Segura and during the internship the main focus was on two objectives: Dissemination of the research and space telecommunications activities for kids and finding ways to dismantle the barriers that prevent girls from becoming engineers.

With the assistance of Lynn, REVOLVE Administrator, Juline set up the Revolve Outreach website, developing a website that is more accessible for the younger audience. Juline also created a series of short videos that explain what a satellite is and how it moves in orbit. She included some videos promoting women for engineering along with an additional video of Herve Legay, Technical Director at Thales Alenia Space (France), presenting the Revolve project. Juline also suggested the communication project ‘Space for Kids’, the objective of which is to create a regular link with young pupils throughout Europe and their research team. Some details surrounding Space for Kids and the PhD students have already been presented on REVOLVE Outreach.

The REVOLVE group agree that it will be a great platform to carry out their dissemination activities, and give sense to the scientific adventure! It will be also a great opportunity for the kids to follow our group of researchers, learn more about space, and hopefully encourage them to consider engineering as a vocation. This link could be implemented with the use of social networks and we have planned a competition which will include ludic activities. Juline hopes that this project will interest the wider public and that both the kids and students will be happy to take part in the exciting initiative!!